Control systems and methods for power amplifiers operating in envelope tracking mode

ABSTRACT

Control systems and methods for power amplifiers operating in envelope tracking mode are presented. A set of corresponding functions and modules are described and various possible system configurations using such functions and modules are presented.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. provisional applicationNo. 61/747,009 entitled “Amplifier Dynamic Bias Adjustment for EnvelopeTracking” filed on Dec. 28, 2012 and incorporated herein by reference inits entirety. The present application also claims priority to U.S.provisional application No. 61/747,016 entitled “Optimization Methodsfor Amplifiers with Variable Supply Power” filed on Dec. 28, 2012 andincorporated herein by reference in its entirety. The presentapplication also claims priority to U.S. provisional application No.61/747,025 entitled “Amplifiers Operating in Envelope Tracking Mode orNon-Envelope Tracking Mode” filed on Dec. 28, 2012 and incorporatedherein by reference in its entirety. The present application also claimspriority to U.S. provisional application No. 61/747,034 entitled“Control Systems and Methods for Power Amplifiers Operating in EnvelopeTracking Mode” filed on Dec. 28, 2012 and incorporated herein byreference in its entirety.

The present application is related to U.S. application Ser. No.13/829,946 entitled “Amplifier Dynamic Bias Adjustment for EnvelopeTracking” filed on even date herewith and incorporated herein byreference in its entirety. The present application is also related toU.S. application Ser. No. 13/830,070 entitled “Optimization Methods forAmplifiers with Variable Supply Power” filed on even date herewith andincorporated herein by reference in its entirety. The presentapplication is also related to U.S. application Ser. No. 13/830,680entitled “Amplifiers Operating in Envelope Tracking Mode or Non-EnvelopeTracking Mode” filed on even date herewith and incorporated herein byreference in its entirety.

BACKGROUND

1. Field

The present application relates to amplifiers operating in an envelopetracking mode. In particular the present application relates to controlsystems and methods for amplifiers operating in the envelope trackingmode.

2. Description of Related Art

Although nonlinear amplifiers can exhibit higher efficiency than linearamplifiers, until recently nonlinear power amplifiers were undesirablefor use with RF signals produced by linear modulation schemes. Atechnique known as “envelope tracking” (ET) was developed that allowsuse of linear amplifiers to approach the efficiency of non-linear poweramplifiers with RF signals produced by linear modulation schemes (e.g.where it is important to maintain relative variation within an envelopeof an RF signal). By dynamically adjusting a DC bias voltage at a drainterminal of an output transistor of a power amplifier in a manner thatroughly follows a time varying envelope of the RF signal, a signalproduced by a linear modulation scheme can be amplified by a poweramplifier without undesirable envelope distortion. Effectively, thetechnique of envelope tracking shifts a burden of linearity away fromthe power amplifier to an ETPS (envelope tracking power supply) that isconnected to the drain terminal of the output transistor of thenonlinear power amplifier.

SUMMARY

According to a first aspect of the present disclosure, a system foraffecting operation of an envelope tracking (ET) amplifier is presented,the system comprising: an ET amplifier configured to receive an RF inputsignal and generate therefrom, an RF output signal based on a responseof the ET amplifier; and a set of operating parameters defining theresponse of the ET amplifier; a control circuit adapted to detect anenvelope of the RF input signal and generate based on said envelopesignal a set of input-control signals that is provided to the ETamplifier for affecting the response according to the set of operatingparameters.

According to a second aspect of the present disclosure, a method forgenerating control signals to affect operation of an ET amplifier basedon a desired response is presented, the method comprising: providing anET amplifier configured to receive a drain control signal and aplurality of gate control signals; generating the drain control signalbased on an envelope signal of an RF input to the ET amplifier;correlating a response of the ET amplifier with the plurality of gatecontrol signals and the drain control signal; generating a correlationtable based on the obtained correlation; selecting operating parametersfor a desired response of the ET amplifier; using the correlation tableto generate a mapping table between the drain control signal and thegate control signals for the desired response; implementing controlcircuitry adapted to generate the gate control signals from the draincontrol signal using the mapping table, and affecting operation of theET amplifier by feeding the drain control signal and the mapped gatecontrol signals generated by the control circuitry to the ET amplifier.

According to a third aspect of the present disclosure, a method forincreasing stability in an amplifying arrangement is provided, themethod comprising: providing a first ET amplifier; providing a second ETamplifier; serially coupling the first ET amplifier to the second ETamplifier, the first ET amplifier configured to receive an input signalof the amplifying arrangement and the second ET amplifier configured tooutput an output signal of the amplifying arrangement; providing an ETpower supply (ETPS) configured to supply a common power to a first powersupply terminal of the first ET amplifier and to a second power supplyterminal of the second ET amplifier; modulating the common power incorrespondence of an envelope signal of the input signal to the first ETamplifier; inserting a filter in a conduction path between the firstpower supply terminal and the second power supply terminal; based on theinserting, attenuating an undesired coupling between the first ETamplifier and the second ET amplifier; based on the attenuating,increasing stability of the amplifying arrangement, such as to reduceoscillation at the output signal of the amplifying arrangement.

According to a fourth aspect of the present disclosure, a method forreducing distortion in an amplifying arrangement is provided, the methodcomprising: providing a first ET amplifier configured to output anamplified input signal at a first output terminal, the input signalbeing fed to a first input terminal; providing a second ET amplifierconfigured to receive an input signal at a second input terminal;serially coupling the first ET amplifier to the second ET amplifier, thefirst ET amplifier configured to receive an input signal to theamplifying arrangement, the second ET amplifier configured to output anoutput signal of the amplifying arrangement; providing an ET powersupply (ETPS) configured to supply power to the first ET amplifier andto the second ET amplifier; modulating the power in correspondence of anenvelope signal of the input signal to the amplifying arrangement;inserting a filter in a conduction path between the first outputterminal and the second input terminal; based on the inserting,attenuating an undesired coupling between the first ET amplifier and thesecond ET amplifier; based on the attenuating, reducing distortion atthe output signal of the amplifying arrangement.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description of exampleembodiments, serve to explain the principles and implementations of thedisclosure.

FIG. 1 shows an example embodiment according to the present disclosureof an envelope tracking amplifier with a match circuit at its output.

FIG. 2 shows an example implementation of an envelope detector.

FIGS. 3-4 show example alternative embodiments to the envelope trackingamplifier shown in FIG. 1.

FIG. 5 shows waveforms that correspond to an exemplary envelope signaland an exemplary control signal that closely follows peaks of theexemplary envelope signal and is slightly higher than troughs of theexemplary envelope signal.

FIGS. 6-7 show example embodiments according to the present disclosureof an envelope tracking amplifier that is configured such that gate biasvoltages applied to gates of different FETs can be independent of eachother due to inclusion of gate modifiers.

FIG. 8 shows an embodiment according to the present disclosure of anenvelope tracking amplifier that is configured such that the gate biasvoltages are supplied by a source (not shown) other than an ETPS (e.g.variable DC-DC converter).

FIG. 8A shows the exemplary embodiment of FIG. 8 for a case where Nstacked devices are used in the amplification stage, where N is largerthan three.

FIG. 8B shows an exemplary embodiment according to the presentdisclosure of an ET configuration where special bias and matchingcircuits are used at the gates of the transistor devices.

FIG. 9 shows an example embodiment according to the present disclosureof an envelope tracking amplifier with gates and drain modulation,wherein summing resistors are used to provide incremental corrections togate biases in addition to gate biasing provided by the ETPS unit.

FIGS. 10-11 show example embodiments according to the present disclosureof an envelope tracking amplifier that is configured to introducevarious phase shifts between the dynamic voltage applied to the drainand the dynamic bias voltages applied to the gates.

FIG. 12 shows an example embodiment according to the present disclosureof an envelope tracking amplifier that can phase shift a bias input tothe gate of the first FET.

FIG. 13 shows an example embodiment according to the present disclosureof an envelope tracking amplifier wherein the ET power supply is avariable current source.

FIG. 14 shows an example embodiment according to the present disclosureof a differential input envelope tracking amplifier wherein the ET powersupply is a variable current source.

FIG. 15 shows an example embodiment according to the present disclosureof a combined output envelope tracking amplifier, wherein transformersare used to combine outputs of the various transistors of a stack.

FIG. 16 shows an example embodiment according to the present disclosureof a transformer-coupled envelope tracking amplifier, whereintransformers are used to couple the various input gates of transistorsof a stack to an input signal.

FIG. 17 shows an example embodiment according to the present disclosureof an envelope tracking amplifier with push-pull output stage.

FIG. 18 shows a differential input/output configuration of theembodiment of FIG. 15.

FIG. 19 shows an exemplary relationship between an RF input signal, acorresponding envelope signal, a corresponding ET power supply controlsignal and a corresponding ET power supply output.

FIG. 20 shows embodiments where a feedback network and a tunablematching network are connected to an amplifier arrangement comprising aplurality of amplifiers, each amplifier being provided with its ownpower source, used to bias the amplifier and to provide power to theamplifier. Each amplifier of FIG. 20 may operate in either an ET or anon-ET mode.

FIGS. 21-22 show alternative embodiments where the feedback network canbe arranged in different locations within the amplifier arrangementcompared to FIG. 1.

FIG. 23 shows an alternative embodiment where a feedback network and atunable matching network are connected to each of the amplifiers withinthe amplifier arrangement.

FIG. 24 shows an embodiment of the present disclosure where a feedbacknetwork is connected to an amplifier arrangement, each amplifier sharinga common power source.

FIG. 25 shows an embodiment where a variable feedback resistor is usedfor further flexibility in tuning the feedback network. In particular,instead of using a switch as depicted in FIGS. 21-22 and FIG. 24, thevariable resistor can be used to reduce the effect of the feedbacknetwork by being set at a high value.

FIG. 26 shows relationships between input/output power and variousregions of operation of an amplifier.

FIG. 27 shows an example of an envelope signal, associated amplifiersupply power and region of operation for an amplifier operating in anenvelope tracking mode.

FIG. 28 shows an exemplary method of detecting a switch control signalas well as the relationship between a switch control, the feedback loopstatus (open/close) and the envelope signal.

FIG. 29 shows relationship amongst various signals used in the proposedembodiment.

FIGS. 29A and 29B contrast the dissipated power in an amplifieroperating in a linear region where the supply power is fixed, versus anamplifier operating in a compression region where the supply powerfollows the envelope of the input RF signal.

FIG. 29C contrasts the Power-Added Efficiency (PAE) of an amplifieroperating in a linear region at different fixed supply voltages versusan amplifier operating in a compression region where the supply powerfollows the envelope of the input RF signal.

FIG. 30 shows an exemplary system configuration for proposed embodiment,wherein a transceiver is used as main controller.

FIG. 31 shows an alternative embodiment with a fixed feedback loop inaddition to the switchable feedback network.

FIG. 32 shows an alternative embodiment with a fixed feedback loop and aswitchable feedback network with an additional network in series.

FIG. 33 shows an embodiment of the present disclosure for a tunablefeedback network.

FIG. 34 shows an example embodiment according to the present disclosurewith an envelope tracking amplifier (e.g. the envelope trackingamplifier shown in FIG. 1 or 8), an envelope detector and a controlunit.

FIGS. 35-37 shows different embodiments according to the presentdisclosure used to configure an envelope tracking amplifier between ETand non ET mode.

FIG. 35 uses an input tunable matching network and an output tunablematching network.

FIG. 36 uses a resistor-capacitor feedback loop that can be enabledthrough the use of a feedback switch.

FIG. 37 uses an alternative resistor-capacitor feedback loop that isconfigured to tune the resistor and capacitor elements based on adesired mode of operation.

FIG. 38 shows an embodiment according to the present disclosure with aninput terminal, a first amplifier, a first switch, a second amplifier, athrough circuit, a third amplifier, a second switch and an outputterminal.

FIG. 39 shows an embodiment according to the present disclosure with aninput terminal, a first amplifier, a second amplifier, a path with aswitch, and an output terminal.

FIG. 40 shows an alternative embodiment of FIG. 39, where a switch canenable one of two different paths comprising amplifiers, each pathhaving different amplification.

FIG. 41 shows an embodiment according to the present disclosure of aswitchable gate bias network that can be connected, for example, to thesecond FET shown in FIG. 1.

FIG. 42 shows the embodiment of FIG. 41 with the additional feature ofan adjustable resistance.

FIG. 43 shows the embodiment of FIG. 41 with the additional features ofadjustable resistance and capacitance.

FIG. 44 shows an embodiment according to the present disclosure of atunable gate bias network that can be connected, for example, to thesecond FET or the third FET shown in FIG. 1 or 8.

FIG. 45 shows an embodiment according to the present disclosure with thetunable gate resistor, the gate resistor switch, the tunable gatecapacitor, and the gate capacitor switch that are shown in FIGS. 40-44.

FIG. 46 shows an embodiment according to the present disclosure of aswitchable gate network that can be connected to any FET, including afirst FET of an envelope tracking amplifier (e.g. the first FET of theenvelope tracking amplifier shown in FIG. 1) to which an input signal(e.g. an RF signal) is applied.

FIG. 47 shows an embodiment according to the present disclosure of atunable gate network that can be connected to any FET, including a firstFET to which an input signal (e.g. an RF signal) is applied (e.g. thefirst FET in FIG. 1 or 8).

FIG. 48 shows an embodiment according to the present disclosure with thegate resistor switch and the tunable gate resistor that are shownindividually in FIGS. 46 and 47, respectively.

FIG. 49 shows an embodiment according to the present disclosure of analternative biasing arrangement for the third FET shown in FIG. 1.

FIG. 50 shows an embodiment according to the present disclosure of aswitchable biasing arrangement applied to the second FET of FIG. 1.

FIG. 51 shows an embodiment according to the present disclosure of anarrangement comprising a first stack of three FETs, a second stack oftwo FETs, a switch that can be operated to select one of the two stacks,an inductor, and an Envelope Tracking Power Supply (ETPS) that isconnected to a voltage supply V_(DD), where the inductor serves as an RFchoke and is placed in a path between the ETPS converter and whicheverstack is selected.

FIG. 52 shows an embodiment similar to FIG. 51, except that the switchused to select one of the two stacks is placed prior to the RF choke(thereby requiring separate RF chokes for each stack).

FIG. 53 shows an exemplary embodiment of the present disclosure whereina DAC unit is used to generate controlling signals.

FIG. 54 shows an exemplary embodiment of the present disclosure whereinseveral DAC units are used to generate bias control signals.

FIG. 55 shows an exemplary embodiment of the present disclosure whereina wave shaping unit is used to generate bias control signals.

FIG. 56 shows an exemplary embodiment of various control modules of thepresent disclosure.

FIG. 57 is a representation of embodiment of FIG. 53 highlighting thevarious system functions.

FIG. 58 is a representation of embodiment of FIG. 54 highlighting thevarious system functions.

FIG. 59 is a representation of embodiment of FIG. 55 highlighting thevarious system functions.

FIGS. 60-61 show equivalent system representations according toembodiment of FIGS. 53 and 57.

FIGS. 62-64 show equivalent system representations according toembodiment of FIGS. 54 and 58.

FIGS. 65-67 show equivalent system representations according toembodiment of FIGS. 55 and 59.

FIG. 68 shows an example embodiment according to the present disclosureof a driver ET amplifier feeding the final ET amplifier, wherein asingle output form an ETPS unit provides the supply to both ETamplifiers.

FIG. 69 shows an example embodiment according to the present disclosureof a driver ET driver ET amplifier feeding the final ET amplifier,wherein two decoupled outputs from a single ETPS unit are used to eachprovide the supply to each ET amplifier.

FIG. 69A shows an example embodiment according to the present disclosureof an amplifier configuration adapted to pass DC and the envelopemodulation frequency components of the ETPS output and stop higherfrequency components of the ETPS output susceptible to put thecombination of a driver ET amplifier and a final ET amplifier intooscillation.

FIG. 70 shows an example embodiment according to the present disclosureof a driver ET amplifier feeding the final ET amplifier, wherein thesupply to each ET amplifier is provided via a dedicated ETPS unit.

FIG. 70A is an equivalent representation of the embodiment of FIG. 70,wherein each amplifier is depicted in more details.

FIG. 70B shows an example embodiment according to the present disclosureof a an amplifier configuration adapted to remove undesirable couplingbetween the various gain stages.

FIG. 71 shows an example embodiment of a waveform generator modulewherein one of many lookup tables is selected to generate the outputwaveform.

FIG. 72 shows an example embodiment of a waveform generator modulewherein a partitioned ROM is used to store the waveform data.

FIG. 73 shows an example embodiment of a waveform generator module usinga Digital Signal Processor.

FIG. 74 shows an example embodiment according to the present disclosurewherein the ET amplifier further comprises Non-Volatile RAM (NV-RAM),temperature detector and other transducers used to report operatingcharacteristics of the amplifier.

DETAILED DESCRIPTION

The present disclosure describes control systems and methods for poweramplifiers operating in envelope tracking mode. Furthermore,configuration methods and arrangements using such amplifiers as well asrelated system integration and controls are presented. Such amplifiersmay be used within mobile handsets for current communication systems(e.g. WCMDA, LTE, etc. . . . ) wherein amplification of signals withfrequency content of above 100 MHz and at power levels of above 50 mW isrequired. Such amplifiers may also be used to transmit power atfrequencies and to loads as dictated by downstream splitters, cables, orfeed network(s) used in delivering cable television service to aconsumer, a next amplifier in an RF chain at a cellular base station; ora beam forming network in a phased array radar system, and other. Theskilled person may find other suitable implementations for the presentdisclosure, targeted at lower (e.g. audio) frequency systems as well,such as audio drivers, high bandwidth laser drivers and similar. Assuch, it is envisioned that the teachings of the present disclosure willextend to amplification of signals with frequency content of below 100MHz as well.

Throughout the present disclosure, embodiments and variations aredescribed for the purpose of illustrating uses and implementations ofinventive concepts of various embodiments. The illustrative descriptionshould be understood as presenting examples of the inventive concept,rather than as limiting the scope of the concept as disclosed herein.

Throughout the present disclosure, the terms “linear region” and“compression region” refer to basic operations of an amplifier stage.When operating in the linear region, the amplifier output response islinear, in other words, the change in the output power of the amplifieris linear with respect to a corresponding change in input power. This isthe typical response of the amplifier at low input power levels.Typically there is minimal change in the amplifier's gain or phaseresponse as a function of input power in this region. As the input powerlevel to the amplifier increases and the amplifier output approaches itsmaximum output level, known as the saturation level, the output responseof the amplifier becomes non-linear. In this case, the change in outputpower of the amplifier for a given change in input power decreases asthe output power approaches the saturation level. Once the output powerreaches saturation level, any incremental increase in input power willnot affect the output power level (zero incremental gain), thusremaining at saturation. The transition region between the linear regionand the region of zero incremental gain is referred to as thecompression region of operation of the amplifier. The region of zeroincremental gain wherein the output power remains at the saturationlevel is referred to as the saturation region. One measure of the amountof compression typically used in the industry is the −1 dB compressionpoint. This is the point at which the gain has been reduced by 1 dB.Furthermore, it is common in the industry to refer to the saturationlevel as the −3 dB compression point. FIG. 26 shows the various regionsof operation of an amplifier. Typically the phase response will changealong with the gain as the amplifier starts to compress.

Operating an amplifier from a fixed supply results in degradedefficiency when the peak-to-average ratio of the modulation is large.This is because the supply voltage needs to be high enough toaccommodate the peak, even though most of the time a much lower supplyvoltage could be used. The voltage from the supply that is not neededfor the RF signal is wasted as heat in the amplifier as depicted by FIG.29A, where the supply voltage level is indicated by the top of the graybox and the dissipated heat is represented by the gray area.

One could imagine coarsely following the envelope of the modulatedsignal with a variable power supply. This provides an advantage if thevariable power supply is efficient. The applied variable supply voltagecan be relatively slow or fast compared to the modulation frequency andstill provide a benefit, as all cases would result in less powerdissipated in the amplifier. In this variable supply case, it is assumedthat the supply is always some level above the instantaneous supplyvoltage needed, which means that all amplitude information is from theRF input waveform, and the amplifier remains as a linear amplifier(operates in the linear region). The amplifier would remain as a linearamplifier throughout (constant gain and phase), but may experiencedistortion such as AM-PM (amplitude modulation-to-phase modulation) dueto the supply voltage changes. Although industry standard definitionsdon't exist at this time, some refer to this method as envelopefollowing. The supply is following the envelope at some level, butdoesn't have to follow it exactly. FIG. 29B depicts such a case, wherethe variable power supply follows very closely the envelope of themodulated signal (e.g. transmitted RF), which results in a reduction ofthe dissipated heat.

The next level of improvement comes when the dynamic supply voltage nolonger maintains headroom or some margin between the needed voltage andthe supplied voltage. In this case, the amplitude of the amplifier'soutput is set or limited by the supply voltage. This puts the amplifierin compression at these instants, which typically further improves theefficiency because now the efficiency of the amplifier has improvedalong with the reduced power due to excess voltage wasted as heat.Transition from linear to compressed regions of operation obviouslyresults in reduced gain for the amplifier. Additionally, the phaseresponse often changes as this transition occurs. The transition fromcompression to linear regions of operation will have the equal butopposite change in gain and phase.

Operating in this mode where the envelope signal from the dynamic supplyputs the amplifier into compression means that the output of the dynamicsupply must be exact in time or phase and also amplitude, otherwisedistortion will result at the output of the amplifier. In other words,the amplitude or envelope path is separate from the phase path, but bothmust have acceptable time alignment when the two components arecombined. This time alignment must be preserved over the bandwidth ofthe modulation, thus imposing limits on the phase distortion allowed inthe paths.

The bandwidth of the envelope signal needs to be several times largerthan the baseband modulation bandwidth. This is because a polardecomposition of the modulation into magnitude and phase shows muchwider bandwidth for the amplitude portion. Another way to think of it isby considering the modulation in an IQ constellation format. Atransition from one symbol to the next may make a phase change of up to180 degrees, but it may go from the outermost symbol's amplitude,through a peak, then approach or even reach zero, and return to anoutermost symbol's amplitude, all within one symbol transition. Thattranslates into a fast amplitude component. This mode of operation,where the envelope must track the signal amplitude precisely, is oftenreferred to as envelope tracking.

In the envelope tracking case, the amplitude and phase information arebeing supplied at the input to the amplifier (complex modulation). Thedynamic supply voltage may further set the amplitude, but isn't requiredat all signal levels. The dynamic supply voltage may apply the envelopesignal at the peaks and through some portion of the modulation, but thenreach a minimum value and let the amplitude information at theamplifier's input continue to provide the amplitude or envelope throughother portions of the modulation. This minimum value of the dynamicsupply is typically chosen based on the capabilities of the dynamicsupply and also the minimum acceptable supply voltages for theamplifier.

If the supply were to follow the envelope all the way through everysymbol transition and thus impart all amplitude modulation through theenvelope path, the result would be a polar modulator. A polar modulatoror polar amplifier has all phase information applied at one port,usually the RF input of an amplifier, and all amplitude informationapplied at a second port, usually the output bias for an amplifier.Polar modulators or amplifiers are challenging for several reasons: 1)the bandwidth of the amplitude signal is much wider than the basebandmodulation and wider than the ET envelope bandwidth, 2) the amplitudesignal may approach or even reach zero in the modulation, which isdifficult to do in a real amplifier setup without significantdistortion, and 3) it is difficult to create a modulated signal over alarge range of output powers.

It should be noted that although envelope tracking is used throughoutthe current disclosure to showcase the various embodiments, many of theteachings of the present disclosure apply not only to envelope tracking,but to envelope following, average power tracking, and polar modulationas well.

Memory effects are also important in amplifiers. Memory effects are whenthe response of the amplifier is dependent on a previous state of theamplifier. For example, if the input modulation hits a peak and causesincreased power dissipation in the amplifier device, the device mayexperience self-heating or a device temperature increase from the powerdissipation. If the modulation amplitude decreases a moment later, theamplifier's gain and phase may still be altered due to the heatingassociated with the modulation from the previous time. There are manypossible sources of memory effects, including thermal, bias circuits,and matching components. Operation in envelope following, envelopetracking, and polar modulation modes can further introduce memoryeffects due to the dramatically changing bias conditions. These effectsmust be considered by the amplifier and system designers.

FIG. 1 shows an example envelope tracking amplifier (100) according tovarious embodiments of the present disclosure. By way of example and notof limitation, the envelope tracking amplifier (100) can comprise astack of FETs (e.g., three FETs): a first FET (115), a second FET (120),and a third FET (155). Moreover, the first FET (115) can be referred toas a first subset of FET(s), and the second FET (120) and the third FET(155) (cascode) can be referred to as a second subset of FET(s). Theskilled person will note that FETs (115), (120) and 155) are configuredas a three-stage cascode amplifier (750). Teachings from otherdocuments, such as U.S. Pat. No. US2011/0181360 A1, published on Jul.28, 2011, further describe stacked cascode amplifiers and methods tominimize output signal distortion by way, for example, of biasing thevarious gates of the transistors within the stack. The person skilled inthe art may use these teaching for further specifics on multi-stagestacked transistors in a cascode configuration. If the stack of FETscomprises more than three FETs, e.g., four FETs, the second, third, andfourth FETs will be considered as part of the second subset of FET(s).In the embodiment shown in FIG. 1, a DC bias voltage is supplied to theenvelope tracking amplifier (100) by a supply voltage V_(DD) (185).Although N-type MOSFETs are used to describe the embodiments in thepresent disclosure, a person skilled in the art would recognize thatother types of transistors such as, for example, P-type MOSFETs andbipolar junction transistors (BJTs) can be used instead or incombination with the N-type MOSFETs. Furthermore, a person skilled inthe art will also appreciate the advantage of stacking more than twotransistors, such as three, four, five or more, provide on the voltagehandling performance of the amplifier. This can for example be achievedwhen using non bulk-Silicon technology, such as insulated Silicon onSapphire technology. In general, individual devices in the stack can beconstructed using CMOS, silicon germanium (SiGe), gallium arsenide(GaAs), gallium nitride (GaN), bipolar transistors, or any other viablesemiconductor technology and architecture known. Additionally, differentdevice sizes and types can be used within the stack of devices.

An envelope tracking power supply (ETPS) (180), such as, for example, avariable voltage or current source (e.g. variable DC-DC converter), canbe connected to receive power from power supply V_(DD) (185) and outputa dynamic bias voltage to a third resistor (175) with a resistance valuerepresented by R_(D3), and to an inductor (170). The dynamic bias outputfrom the ETPS can be controlled by a control voltage or current signal“ctrl” (190). As a consequence of the control signal (190) applied tothe ETPS (180) the dynamic bias voltages ET_(RD3) and ET_(DR) arefunctions of a time varying envelope of an RF input signal (e.g. FIG.19) that is provided to an input terminal (105) of the envelope trackingamplifier (100). The input port of the envelope tracking amplifier (100)can comprise the input terminal (105) and a reference (e.g. ground)terminal that is connected to a source of the first FET (115). Theenvelope of the RF input signal is hereinafter referred to as an“envelope signal”, and may be represented by a time varying signalroughly following the envelope of the RF input signal. Although avariable DC-DC convertor may be used to describe the ETPS within thevarious embodiments of the present disclosure, a person skilled in theart would recognize that other types of envelope tracking power supplies(ETPS) based on variable voltage or current sources may be used as well.FIG. 19 shows an exemplary relationship between an input RFin signal, acorresponding envelope signal, an ETPS control signal (ctrl) derivedfrom the envelope signal and an output of the ETPS corresponding to thecontrol signal. It is to be noted that during the envelope trackingoperation the ETPS control signal, and thus the ETPS output, at timesfollows the envelope signal, and at times takes a fix value. The personskilled in the art will know that when ETPS output follows the envelopesignal, the output of the amplifier is in compression and the RF outputpower is provided by the ETPS, and when at a fixed level, the amplifieroperates linearly and the RF output is determined by the RF inputsignal.

Envelope tracking power supplies need to have a bandwidth wide enough tosupport the amplitude component of the modulation. As mentioned, thiscan be many times greater than the baseband bandwidth. To accomplishthis, many ETPSs are built using a combination of a DC-DC switchingconverter and an analog error amplifier. They can be constructed in manyways, including serial and parallel combinations. The switching DC-DCconverter is typically more efficient than the analog amplifier, but hasa more limited bandwidth. This is because the DC-DC converter cansupport a modulation bandwidth that is approximately a factor of 5 to 10lower than its switching frequency. Faster DC-DC converters are desired.The process choice plays an important role in setting the bandwidth ofthe DC-DC converter. While hybrid technologies such as CMOS (controlcircuits) and GaN (switchers) might offer high speed and efficiency,monolithic integration benefits such as cost and size may push thesolution to a process such as CMOS, CMOS SOI, or CMOS SOS. The benefitsof the SOI and SOS processes include a variety of benefits, one of whichis lower parasitic capacitance, and thus faster speeds. If the DC-DCconverter is fast enough, the analog amp would not be required.

There are numerous benefits to integration of these functions and evenintegration with the amplifier itself. Integration of the ETPS orportions of it with the amplifier can result in reduced parasiticinductance, reduced parasitic capacitance, reduced phase delays anddistortion, and device matching. With monolithic integration of circuitblocks that may include the amplifier, ETPS, and/or control circuits,one can make use of the matching between devices to track and adjustvariations due to manufacturing tolerances, temperature and others inways that can't be supported across multiple ICs and possibly multipletechnologies.

The term “port” refers to a two terminal pair, where a signal can beapplied across the two terminals. As used herein, the term “dynamic biasvoltage” may refer to a bias voltage that can vary with respect to time.The envelope signal may be extracted from the RF input signal by way ofan envelope detector. FIG. 2 shows an example implementation of theenvelope detector (1100). The envelope detector (1100) can comprise adiode (1120) in series with a load, where the load can be represented bya capacitor (1140) with a value of C_(env) and a resistor (1150) with avalue represented by R_(env) that are connected in parallel. R_(env) andC_(env) can be chosen to determine a maximum rate change of an envelopesignal RF_(envelope) that is extracted at an output terminal (1130) froman input signal RF_(in) that is fed into an input terminal (1110).Further design details of the envelope detector (1100) as well as otherimplementations of envelope detectors will be known to a person skilledin the art.

Turning back to FIG. 1, the inductor (170) serves as an RF choke toallow the dynamic bias voltage ET_(DR) to pass to a drain of the thirdFET (155) while preventing RF energy from flowing to the ETPS (180). Theinductor (170) in FIG. 1 can be a choke, a smaller inductor that is partof the matching circuit, or a more complex structure that diplexessignals at different frequencies. A coupling capacitor (160) isconnected between the drain of the third FET (155) and an outputterminal (165) where an RF output signal can be obtained. An output portof the envelope tracking amplifier (100) can comprise the outputterminal (165) and the ground terminal that is connected to the sourceof the first FET (115). This output port typically feeds a matchingcircuit (166) (e.g. tunable matching network as described in U.S. Pat.No. 7,795,968 B1, issued on Sep. 14, 2010, which is incorporated hereinby reference in its entirety) to condition the RF output signal for thenext stage. The third resistor (175) is further connected to a gateresistor (144), which is connected to the gate of the third FET (155). Asecond resistor (140) with a value represented by R₃₂ is connectedbetween node (145) and a second gate resistor (134), which is connectedto the gate of the second FET (120). A first resistor with a valuerepresented by R₂₀ is also connected between electrical ground and node(135). The value of the gate resistor (144) may be smaller than thevalue of resistor (175) and the value of gate resistor (134) may besmaller than the value of resistor (140). By way of example and not oflimitation, gate resistors (144) and (134) may be 50 ohms.

The third, second, and first resistors (175), (140), and (130),respectively, form a voltage divider network such that a set of biasvoltages ET_(G2), ET_(G3) are scaled versions of the dynamic biasvoltage ET_(RD3) and therefore vary as a function of the envelopesignal. For example, the bias voltage ET_(G2) can be expressed accordingto the following equation as per standard voltage division:ET_(G2)=ET_(RD3)*(R ₂₀)/(R ₂₀ +R ₃₂ +R _(D3)).The voltage divider network may be considered to be an exampleembodiment of bias adjustment circuitry. As used herein, the term “biasadjustment circuitry” may refer to circuitry that is configured toperform an adjustment operation on a dynamic bias voltage signal priorto applying the dynamic bias voltage signal to bias terminals of anamplifier that comprises stacked FETs. In the embodiment shown in FIG.1, a third gate capacitor (150) is connected between the gate of thethird FET (155) and electrical ground. Also in the embodiment shown inFIG. 1, a second gate capacitor (125) is connected between the gate ofthe second FET (120) and electrical ground. The gate capacitors (125,150) allow gate voltages (voltage across the respective gate capacitor)of the second FET (120) and the third FET (155), respectively, to float,that is let the gate voltages vary along with the RF signal at the drainof the corresponding FETs (120, 155), which consequently allow control(e.g. evenly distribute) of the voltage drop across the two transistorsfor a more efficient operation of the two transistors. See for example,U.S. Pat. No. 7,248,120, issued on Jul. 24, 2007, entitled “StackedTransistor Method and Apparatus”, which is incorporated herein byreference in its entirety.

During operation of the envelope tracking amplifier (100), a biasvoltage at the drain of the third FET (155), delivered through theinductor (170), in addition to the bias voltages ET_(G2) and ET_(G3) atthe gate of the second FET and the gate of the third FET, respectively,vary as a function of the envelope signal as dictated by the ETPScontrol signal (190).

Additionally, a bias voltage ET_(G1) can be applied to a first gate biasnode (110) to bias a gate of the first FET (115). The bias voltageET_(G1) can be either a fixed voltage or a dynamic bias voltage. One ormore of the gate bias voltages ET_(G1), ET_(G2), ET_(G3) can be scaled,amplitude shifted, phase shifted, inverted, and/or subject to anymathematical operation (e.g. implemented by an op-amp circuit) withrelation to the dynamic bias voltage ET_(DR) supplied to the inductor(170), such operations performed by other embodiments of bias adjustmentcircuitry. Introducing a phase shift in one or more of the gate biasvoltages ET_(G1), ET_(G2), ET_(G3) can compensate for unintended effectsof the envelope tracking amplifier (100) by pre-distorting phase(s) ofthe first, second and/or third FET (115, 120, 155). In some embodiments,the bias voltage ET_(G1) is held fixed while the other two bias voltagesET_(G2) and ET_(G3) vary as a function of the envelope signal. In otherpossible embodiments, one or more of the gate bias voltages ET_(G1),ET_(G2), ET_(G3) are dynamic bias voltages while other gate biasvoltages are fixed bias voltages. By way of example, and not oflimitation, FIG. 3 shows an exemplary arrangement of implementing thedynamic bias voltage to the gate of the first FET (115) through thevoltage divider formed by resistors R_(D3), R₃₂, R₂₀, and R₁₀. In someembodiments, the dynamic bias voltage for the drain and the gates of theFETs can come from a single output of the ETPS (180), as shown in FIG.4.

The envelope tracking amplifier (100) can be used as a driver, a final,or any other type of amplifier. For example, such an amplifier may beused within a mobile handset for current communication systems toamplify signals with frequency content above 100 MHz and at power levelsof above 50 mW. The stack of FETs may comprise any number of FETs (e.g.FIG. 8A, described later) and be chosen to be partially or fullydepleted for best overall performance. The embodiment shown in FIG. 1uses three FETs merely by way of example, as a person skilled in the artwill be able to extend the teachings of the present disclosure to otherembodiments comprising any number of FETs in the stack of transistors.The bias for the gate of the first FET (115) can be provided by, forexample, a current mirror circuit, or any of a variety of standardbiasing configurations known to a person skilled in the art.

In some embodiments, the control signal (190), that is used to determinethe dynamic bias voltages ET_(RD3) and ET_(DR), closely follows theenvelope signal. In other embodiments, the control signal (190) closelyfollows peaks of the envelope signal and can be slightly higher than thetroughs of the envelope signal. In yet other embodiments, the controlsignal (190) may alternate between following the envelope signal duringcertain periods of time, and being constant during other periods oftime. FIG. 5 shows waveforms that correspond to an exemplary envelopesignal (210) and an exemplary control signal (190) that closely followspeaks of the exemplary envelope signal and is constant during thetroughs of the exemplary envelope signal. Such an embodiment enables theenvelope tracking amplifier to operate in or near the compression regionof the amplifier during peaks of the envelope signal, and operate in thelinear region of the amplifier during troughs of the envelope signal. Inembodiments where the dynamic bias voltages ET_(RD3) and ET_(DR) aredirectly related (e.g. ET_(RD3) and ET_(DR) both increase or decrease atsimilar times), equal voltage division across the second and third FETs(120, 155) can be maintained, which contributes to keeping the secondand third FETs (120, 155) in saturation as the RF input signal and theRF output signal vary. Modulating the gate voltage (e.g. via ET_(RD3))lets the transistors in the stack remain in the saturation region, thuspreserving their amplitude and phase characteristics as the envelopesignal is varied. This leads to better overall amplifier linearity andthus efficiency.

In some embodiment it may be desirable to modulate the gate voltage viaan envelope signal, such as ET_(RD3), while letting the gate float withthe RF signal as described earlier. In this situation and consideringthe third FET transistor (155), the corresponding gate capacitor (150)and resistor (R144) have to be chosen such as the low pass filter seenby ET_(RD3) passes the entire frequency spectrum of the envelope signal,and at the same time the impedance seen by the RF signal looking fromthe gate of the transistor (e.g. capacitor (150) in parallel withresistor (R144)) is such that the RF signal attenuation is set by thecapacitor as designed and not by the bias and envelope path. Given theseconstraints, derivation of corresponding resistor and capacitor values,as well as derivation of the more generalized formula taking intoaccount for example transistor's model and other components within thecircuit, are well within the reach of the skilled person.

Alternatively, the dynamic bias voltage ET_(RD3) can be inverselyrelated to the envelope signal. As voltage at a drain terminal of thethird FET (155) becomes sufficiently low, the third FET (155) and/or thesecond FET (120) begin(s) to act as a gate voltage controlled resistor(triode) instead of a gate voltage controlled current source(saturation). If the dynamic bias voltage ET_(RD3) becomes high as thethird FET (155) and/or the second FET (120) begin(s) to act as a gatevoltage controlled resistor, an equivalent resistance presented by thethird FET (155) and/or the second FET (120) can become low since anequivalent resistance presented by a FET in triode operation can beinversely proportional to a gate bias voltage of the FET in triodeoperation. As a result, when the dynamic bias voltage ET_(RD3) isinversely related to the envelope signal, it is possible that the thirdFET (155) and/or the second FET (120) do(es) not significantly hinderoperation of the envelope tracking amplifier (100) when voltage at adrain terminal of the third FET (155) becomes sufficiently low that thethird FET (155) and/or the second FET (120) begin(s) to act as a gatevoltage controlled resistor (triode).

FIG. 6 shows an embodiment according to the present disclosure of anenvelope tracking amplifier (300) that is configured such that the gatebias voltages applied to node (145) and node (135) can be independent ofeach other due to inclusion of a third gate modifier (310) and a secondgate modifier (320), both of which, alone or in combination, are exampleembodiments of bias adjustment circuitry. The third gate modifier (310)and the second gate modifier (320) can comprise circuits that areconfigured to independently scale, amplitude shift, phase shift, invert,and/or perform any mathematical operation (e.g. implemented by an op-ampcircuit) of the dynamic bias voltage ET_(G32) to generate the gate biasvoltages ET_(G3) and ET_(G2) that are adapted to be applied to node(145) and node (135), respectively. The first gate (ETG₁) can be biasedby, for example, a current mirror circuit connected to the gate of thefirst FET (110). Compared to the embodiment shown in FIG. 1, theembodiment shown in FIG. 6 provides additional freedom because voltagesET_(G3) and ET_(G2) are not tied together by a resistive voltagedivider.

FIG. 7 shows an alternative embodiment where the gate of the first FET(115) can also be biased by a first gate modifier (330) in substantiallya similar manner as the second gate modifier (320) and the third gatemodifier (310). In some embodiments, the gate modifiers (310, 320, 330)can be made of a variety of analog or digitally tuned circuits known bythose skilled in the art. By way of example and not of limitation, thegate modifiers (310, 320, 330) can be a simple op amp circuit, or an RLCcircuit.

FIG. 8 shows an embodiment according to the present disclosure of anenvelope tracking amplifier (800) that is configured such that the gatebias voltages applied to node (145) and node (135) are supplied by asource (not shown) other than the ETPS (180). By way of example, and notof limitation, the source other than the ETPS (180) may comprise abaseband controller such as a transceiver unit (not shown). The basebandcontroller can be a part of an RF circuit that comprises the envelopetracking amplifier (800). Regardless of the method of supply of the gatebias voltage (e.g. to nodes (135), (145)), when operating in theenvelope tracking mode, usually such gate bias voltage would share thecharacteristic of varying as a function of the envelope signal (e.g.FIG. 27). In some cases however, even though ET operation is desired, itmay be desirable not to vary all of the gate bias voltages, as any oneof the gates, including the gate of the input transistor (115), may beheld at fixed voltage during ET operation. This selection, oroptimization of gate bias voltage, is based on device choices,corresponding devices breakdown voltages, the choice of DC biasconditions, and voltage division through the stack, among other things.

FIG. 8A depicts the embodiment of FIG. 8 for a case where the number ofstacked devices in the amplifier is n, where n is larger than three. Theconfiguration of FIG. 8A allows the envelope tracking amplifier 800A tobe fed (n−1) gate bias voltages via nodes 135 ₁ through 135 _((n-1)). Aspreviously mentioned, configurations with stacked higher than threedevices can be applied to any of the embodiments of the presentdisclosure, and is not limited to FET devices only. Transistors in thestack can be of different sizes (e.g. oxide thickness) and types (e.g.different threshold voltages).

In some embodiments it may be desirable to replace the R-C networks(e.g. 134, 125 of FIG. 8A) at the gate of the cascode devices (orequivalent) with a different circuitry and as suited by theconfiguration. FIG. 8B shows such an embodiment according to the presentdisclosure, wherein the R-C networks at the gates are replaced withapplication specific biasing and matching circuits (136). These circuitsmay include a combination of active and passive devices and shape theinput gate bias voltage ETG at terminals (135) to an effective gate biasvoltage as required by the desired mode of operation of the ETamplifier. These circuits may operate at frequencies ranging from DC tothe RF modulation frequency.

In some embodiments, the baseband controller can be used to generate theenvelope signal, whether from the baseband signal or directly from theRF signal. Furthermore, the baseband controller can generate the gatebias voltages ET_(G1), ET_(G2), and ET_(G3) in a manner similar to theembodiments previously discussed by scaling, amplitude shifting, phaseshifting, inverting, and/or performing any mathematical operation (e.g.implemented by an op-amp circuit or digital signal processors) on theenvelope signal. By way of example, and not of limitation, digitaltechniques (e.g. look-up tables, D/A and A/D converters) can be used togenerate arbitrary voltage signals that are then used as the gate biasvoltages ET_(G1), ET_(G2), and ET_(G3). Analog circuit techniques may beused to generate arbitrary voltage signals (including fixed voltages)that can then be used as the gate bias voltages ET_(G1), ET_(G2), andET_(G3) as well. Example embodiments of such configurations can be foundin FIGS. 53-70, which will be described in detail in later paragraphs.

FIGS. 10-11 show example alternate embodiments of an envelope trackingamplifier (500) that is configured to introduce both a phase shiftand/or amplitude changes in the dynamic bias voltage ET_(RD3) prior tothe dynamic bias voltage ET_(RD3) being applied (by way of acapacitive-resistive network) to the gate of the third FET (155) andbeing applied (by way of an inductive-resistive network) to the gate ofthe second FET (120) as the dynamic gate bias voltages ET_(G3) andET_(G2), respectively. The capacitive-resistive network and theinductive-resistive network, alone or in combination, are furtherexample embodiments of bias adjustment circuitry. In comparison with theembodiment shown in FIG. 1, a capacitor (510) (e.g., a variablecapacitor, digitally tunable capacitor) with a value represented by C₃has been connected between the third resistor (175) and the ETPS (180)(e.g. variable voltage or current source). Additionally, a third gateresistor (520) with a value represented by R_(G3) has been connectedbetween node (145) and a DC voltage V_(DC3).

The embodiments shown in FIGS. 10 and 11, as well as FIGS. 6, 7, and 8Ballow for the ability to adjust the amplitude and phase of the envelopesignal applied to the gates. This can be used as a modulation port forimparting modulation, or for a pre-distortion method to compensate fordistortion in the amplifier. This is true for all modes of operation(linear, envelope following, envelope tracking, polar, and other modes).

The capacitor (510) may block a DC component of the dynamic bias voltageET_(RD3) and pass a time-varying component of the dynamic bias voltageET_(RD3). The DC voltage V_(DC3) can restore the DC component of thedynamic bias voltage ET_(RD3) to the gate of transistor (155). In asimilar manner, V_(DC2) can restore the DC component to the gate oftransistor (120). The embodiment of FIG. 10 thus allows application ofthe DC component of the gate bias supplies separately from the dynamiccomponent representing the envelope signal.

Capacitor (510) may be used to create a desired phase shift between thedynamic bias voltage ET_(RD3) and the third gate bias voltage ET_(G3).Circuit analysis that accounts for the resistor (520), the third gatecapacitor (150), possibly a parasitic gate capacitance of the third FET(155), and other components surrounding node (145) to derive an equationfor the amount of phase shift is within the capability of a personskilled in the art. Results of such analysis can be used to determineappropriate values of C₃, R_(D3), R_(G3), and the third gate capacitor(150) and resistor (144) that can yield a desired phase shift.

With further reference to FIG. 11, the inductive-resistive networkcomprises an inductor (530) with a value represented by L₃₂ (e.g.,variable inductor, digitally tunable inductor) connected in series witha second resistor (540) with a value represented by R_(D2). Theinductive-resistive network is connected between node (135) and the ETPS(180). A DC bias voltage V_(DC2) may be overlaid to the envelope signalat node (135). The circuit comprising the inductor (530), the secondresistor (540), and the second resistor (130) forms a voltage dividerfrom the dynamic bias voltage ET_(RD3) to the second gate bias voltageET_(G2). Assuming that the voltage source that connects to R_(G2) has alow output resistance when compared with R_(G2), the second gate biasvoltage ET_(G2) that results from such voltage divider can be determinedaccording to the following equation:ET_(G2)=ET_(RD3)*(R ₂₀ //R _(G2)/(R ₂₀ //R _(G2) +R _(D2) +jωL ₃₂)The // sign indicates a parallel combination of resistors where:Rparallel=(R1*R2)/(R1+R2).

Complex number analysis of the equation stated above can reveal that aphase shift in an amount equal to an inverse tangent of a quantityrepresented by ω*L₃₂/(R₂₀+R_(D2)) can occur between the dynamic biasvoltage ET_(RD3) to the second gate bias voltage ET_(G2). A morecomplete analysis that accounts for the second gate capacitor (125) andpossibly a parasitic gate capacitance of the second FET (120) is withinthe capability of a person skilled in the art. Results of such analysiscan be used to determine appropriate values of L₃₂, R_(D2), R₂₀, and thesecond gate capacitor (125) that can yield a desired phase shift.

In other embodiments similar to FIGS. 10-11, phase shifts may beintroduced in signal paths between the ETPS (180) and the gates of thesecond and third FETs (120, 155) by using capacitive-resistive networksin both signal paths, or by using inductive-resistive networks in bothsignal paths. In other embodiments, a capacitive-resistive network canbe used to introduce a phase shift in a signal path between the ETPS andnode (135) while an inductive-resistive network is used to introduce aphase shift in a signal path between the ETPS (180) and node (145).Alternatively, a phase shift may be introduced in a signal path betweenthe ETPS (180) and a gate of one FET from among the second and thirdFETs (120, 155) while the other FET from among the second and third FETs(120, 155) receives a dynamic bias voltage that has not been phaseshifted. A person skilled in the art will not require further diagramsto understand such embodiments.

FIG. 12 shows an embodiment according to the present disclosure of anenvelope tracking amplifier (600) similar to the envelope trackingamplifier (100) of FIG. 1 except for a circuitry being added tointroduce a phase shift in the dynamic bias voltage or current that isapplied to the first gate bias node (110). By way of example and not oflimitation, an inductive-resistive network similar to theinductive-resistive network shown in FIGS. 10-11 is connected betweenthe gate of the first FET (115) and the first gate bias node (110) tophase shift the signal between the first gate bias node (110) and thegate of the first FET (115). The example inductive-resistive networkcomprises an inductor (650) with a value represented by L_(BE1)connected in series with a resistor (640) with a value represented byR_(BE1). Analysis and design of the inductive-resistive networkcomprising the inductor (650) and the resistor (640) is within reach ofthe skilled person.

In some embodiments, a capacitive-resistive network can be connectedbetween the first gate bias node (110) and the gate of the first FET(115). In circuits where the capacitive-resistive network is connectedbetween the first gate bias node (110) and the gate of the first FET(115), a DC voltage can also be applied to the gate of the first FET(115) to restore a DC component of a dynamic bias voltage that isapplied to the first gate bias node (110), in a manner similar to thecapacitive-resistive network shown in FIGS. 10-11.

FIG. 13 shows an example embodiment according to the present disclosureof an envelope tracking amplifier wherein the ET power supply is avariable current source. In this configuration the ETPS (180) is acurrent source, connected to the source terminal of transistor (115),and which modulates the current of the stack via its input controlsignal (190). Main supply power is still provided by V_(DD) (185), nowconnected to the inductor (170). A capacitor (161) is connected betweenthe source terminal of transistor (115) and ground. At RF frequency, theequivalent impedance of the capacitor is very small, effectivelyproviding an RF ground to the source of the transistor. In thisconfiguration, gate biases are controlled in a similar manner as in theprevious cases.

FIG. 14 shows an example embodiment according to the present disclosureof a differential envelope tracking amplifier wherein the ET powersupply is a variable current source. In this configuration the input RFsignal, as well as the various bias supplies, may be provideddifferentially to the corresponding complementary input terminals. It isto be noted that in some cases, nodes ET_(G3+)/ET_(G3−) andET_(G2+)/ET_(G2−) may be connected to create a single gate bias node foreach transistor pair, such as single ended bias supplies may be providedto the gates of the transistor pairs through these nodes. In theembodiment of FIG. 14, node (ET_(I)) is a virtual ground. In general,for all the arrangements disclosed, the source terminal of the inputtransistor is connected to a reference potential of the arrangement,which may be effectively a system reference ground as in FIGS. 1-4, anRF ground as in FIG. 13, or a virtual ground as in FIG. 14.

FIG. 15 shows an example embodiment according to the present disclosureof a combined output envelope tracking amplifier, wherein transformers(T_(n), T_(n-1), . . . , T₁) are used to combine outputs (power) of thevarious transistors (M_(n), M_(n-1), . . . , M₁). In this embodiment theinput RF signal is fed to all the transistors in parallel, which thushave a common input node at their gates. Each transistor is thus biasedsimilarly, by way of the common gate bias voltage (V_(g)), and thevariable supply provided by the ETPS unit to their drains via aplurality of transformer chokes (primary side of the transformer). Inthis configuration, the gate bias voltage may be further modifieddynamically as per prior description (e.g. envelope signal). The personskilled in the art will understand that each of the transistors (M_(n),M_(n-1), . . . , M₁) may be replaced by a cascode configuration forhigher RF output power capability and/or higher gain. Similarly, thesame person may envision a differential implementation of thisembodiment. FIG. 18 shows such an example, wherein differentialinput/output amplifiers in cascode configuration are used.

FIG. 16 shows an example embodiment according to the present disclosureof a transformer-coupled input envelope tracking amplifier, whereintransformers (T_(n), T_(n-1), . . . , T₁) are used to couple the variousinput gates of transistors of a stack to an input RF signal. In thisconfiguration, transistors from the stack are connected in a seriesconfiguration (e.g. source to drain), with power from the ETPS unitconnected to the transistor at the top (M_(n)), and a referencepotential (e.g. ground) connected to the source terminal of the bottomtransistor (M₁). Dynamic gate biasing may be provided via voltages(V_(gn), V_(g(n-1)), . . . , V_(g1)), which with the help of thecapacitors (C_(n), C_(n-1), . . . , C₁) set the gate-to-source voltagesfor each of the transistors. The person skilled in the art will noticethat in this embodiment V_(gn)>V_(g(n-1))> . . . >V_(g1). The personskilled in the art will understand that each of the transistors (M_(n),M_(n-1), . . . , M₁) may be replaced by a cascode configuration forhigher RF output power capability and/or higher gain. Similarly, thesame person may envision a differential implementation of thisembodiment.

FIG. 17 shows an example embodiment according to the present disclosureof an envelope tracking amplifier with push-pull output stage. In thisconfiguration the top of the stack may comprise a number of P-typeMOSFET devices connected in a series configuration, and the bottom maycomprise the same number of N-type MOSFET devices also connected in aseries configuration. The middle two devices are thus of opposite typesand interconnected at their drain terminals. In this embodiment theinput RF is fed to the top and bottom devices, via input couplingcapacitors (162 a, 162 b), which in turn propagates through the top andbottom halves of the stack in a complementary fashion, yielding inoutputting the amplified RF output signal from one half of the stack orthe other half of the stack. In some embodiments both halves may outputsimultaneously but at different power levels. Biasing of the gates maybe provided via fixed voltages, or via dynamic voltages (Vg1, Vg2) asdepicted in FIG. 17 and generated within the ETPS unit. The personskilled in the art will understand that each of the transistors may bereplaced by a cascode configuration for higher RF output powercapability. Similarly, the same person may envision a differentialimplementation of this embodiment.

As previously discussed, in the case of an amplifier configured for EToperation, also referred to as “ET mode of operation”, such amplifier issusceptible to operate in either the linear or the compression region,latter being the desired region of operation. Furthermore, when theamplifier is not configured for ET mode of operation (non-ET mode), forexample by virtue of supplying a fixed supply voltage to the amplifier,the amplifier is also susceptible to operate in either linear orcompression regions, but in such case the desired region of operation isthe linear region.

As discussed in prior sections, ET amplifiers operate as a function ofan envelope of the input RF signal, referred to as the envelope signal,to the amplifier which may be applied to their supply and biasinginputs. The envelope signal can be equivalent to the time varyingtracking signal corresponding to the successive peaks of the input RFsignal. When the output of the amplifier tracks the envelope signal dueto a change in the applied supply level, the amplifier operates mainlyin the highly efficient compression region. When operating in thisregion, the applied supply restores the amplitude of the output which islost due to operation in the compression region of the amplifier (AM/AMdistortion). Alternatively and mainly at low input power levels, theamplifier output follows the envelope of the input RF signal andoperates in the linear region, which is a less efficient region ofoperation typical to non-ET configurations.

One of the main drives for ET implementation within power amplifiers isthe improvement in power efficiency while maintaining a good linearresponse of the amplifier. ET seeks to improve efficiency by adjustingthe supply power based on roughly following the time varying envelopesignal thereby adjusting the supply power to the amplifier based on thepotential demand. Thus less supply power is provided for lower levelinput signals, thereby reducing wasted power provided to the amplifiers.Adjustment of the supply power for ET implementation can be done byeither adjusting the supply voltage (FIGS. 1, 3, 4) to the amplifier orby adjusting the supply current (FIGS. 13-14) to the amplifier. In bothcases, a supply control signal derived from the envelope signal andencompassing desired ET behaviors may be used to dynamically adjust theET supply power.

The supply control signal is constructed using the envelope signal andsuch as to reflect limitations associated with ET mode of operation,such as bandwidth limitation of the dynamic output of the variable powersupply as well as limitations in output linearity of the amplifier atlow power levels when operating in the compression region (e.g. due tolow V_(DS) voltage across one or more of the stack transistors), latterlimitation defining a minimum preset power level for ET mode ofoperation. Additional scaling and offset components are applied to thecontrol signal such as to map the output signal of the amplifier to thedesired operational range.

Even though the amplifier is set to operate in ET mode, there areinstances when the combination of low input RF power level to theamplifier and the ET supply power level (controlled by the supplycontrol signal) removes the amplifier from the compression region andputs it into the traditional linear region of operation typical tonon-ET configurations. This switching from compression region to linearregion of operation and vice versa, is dependent on the modulationscheme used on the input RF signal, but expected to occur especially inRF signals with high peak-to-average power ratio.

FIG. 27 shows an example of an envelope signal and associated amplifiersupply power when operating in ET mode. The supply power follows thetime varying envelope signal (e.g. amplitude varies as a function oftime) during its peaks, pushing the amplifier to operate in compressionand controlling the envelope through the applied envelope voltage. Asthe supply power lowers and reaches its minimum preset level, the supplystops following the envelope signal and thus the amplifier startsoperating in the less efficient linear region wherein the supply levelis static. In an ET mode, the linear region of operation is thuscharacterized by the region wherein the supply power is set to theminimum preset value.

As discussed earlier, operating in the compression region has theadvantage of linearity and reduced power dissipation to some degree.FIGS. 29A and 29B show the level by which the dissipated heat can bereduced between a traditional fixed supply operation depicted by FIG.29A, and a variable supply operation depicted by FIG. 29B (notaccounting for difference in heat dissipation between the power suppliesoperating at these different regions), where the supply closely followsthe envelope signal of the modulation. Going to FIG. 29C, the poweradded efficiency (PAE) versus output power is plotted for the same twocases of operation. During linear operation, for a given fixed supply,the PAE rises with a rise of the output power until the outputeventually saturates (e.g. close to saturation) and the PAE reaches amaximum practical level, for example around 28% at an output power levelof 15.5 dBm for a supply voltage of 1.5 volts. This maximum practicallevel is a function of the fixed supply voltage, and rising the fixedsupply voltage will yield to higher maxima values for the PAE asdepicted by FIG. 29C, where the PAE is plotted for various fixed supplyvoltages, ranging from 1.5 volts to 6 volts. In the case where theamplifier operates in the compression region and with a variable supplyvoltage, the PAE follows the heavy dashed curve, which corresponds at ahigher output power range to the points swept by the maxima of the fixedsupply operation, and at a lower output power range it falls back into alinear operation. This fall back occurs at an equivalent power supplylevel of 1.5 volts. This level is the “minimum level” referenced in FIG.29 and discussed in the following paragraphs.

When the amplifier makes the transition from the compression region tothe linear region, it operates with less power efficiency and with someadded level of distortion to the amplified output as the benefit ofAM/AM amplitude correction via supply power modulation is lost. Anotherundesired side effect of the switching between regions of operation ofthe amplifier is the change in gain at the output of the amplifierstage; when in the compression region the output signal is clipped andthus reduces the gain of the amplifier as compared to the gain obtainedwhen operating in the linear region.

The present disclosure provides systems and methods by which saidlimitations can be overcome or at least reduced by some degree. Forexample, a feedback network can be used within a feedback path around anET amplifier to create a closed loop configuration such as to optimizeresponse when the amplifier is pushed into operating in the linearregion. Given the electrical characteristics of the amplifier,traditional feedback amplifier design techniques can be used to optimizeamplifier performance in the linear region and thus positively affectcorresponding vital parameters such as gain, phase, distortion andstability. This feedback network can be switched in and out, toeffectively activate and de-activate the feedback loop, in unison withthe desired operational mode and/or region of operation of the amplifier(ET versus non-ET modes or compression versus linear regions) and undercontrol of a main controller unit which may be aware of the input RFsignal to the amplifier or the corresponding envelope signal.

One example of this benefit is that by using feedback in the linearregion and removing the feedback in the compressed region is that thegain and efficiency are maximized in the compressed region, whilelinearity is maximized in the linear region. Another example is thatusing feedback in the linear region and removing the feedback in thecompressed region lets one choose how much gain and thus gaincompression (e.g. amount of gain less than the equivalent gain in thelinear region) they want in their system as a design parameter, not justa device property.

In another embodiment further linearization of the amplifier can beobtained by adjusting the various gate bias supplies (e.g. ETG₁, ETG₂,ETG₃ of FIGS. 1, 3-4, 6-14) such as to compensate for changes in thegain curves of individual transistors of the stack as the ET supplypower (e.g. voltage) varies. A controller which is aware of the ETsupply power level or the corresponding controlling signal, incombination with lookup tables (shaping tables) containing transistorcharacteristic data (e.g. current gain characteristic curve.), may beused to create and apply the desired adjustments.

Such a controller mentioned in the above embodiments can be thetransceiver unit traditionally used in modern communication systems. Thecontroller can generate a switch control signal which is synchronized tothe change in operational mode/region of the amplifier. FIG. 30 showssuch an embodiment, wherein the switch control signal is generatedwithin the transceiver unit (2020) and fed to switch control inputterminal (2102). In the embodiment of FIG. 30, the same transceiver unit(2020) generates the supply control signal which in turn is fed to inputterminal (2132) of the ET power supply unit (2130), which latter uses togenerate the effective supply power to the amplifier stage (2115) viaits internal dedicated circuitry (gate input and drain input modules(2025, 2035)).

FIG. 28 shows a relationship between the switch control, the feedbackstatus (open loop, close loop) and the amplifier operating region. InFIG. 28, a comparator unit is used to generate the switch controlsignal, as an alternative method to having a controller, such as oneshown in FIG. 30, perform this task. As shown in FIG. 28, the envelopesignal and a preset minimum value corresponding to the minimum supplypower to the ET amplifier are the inputs to the comparator. In FIG. 28,it is assumed that the switch is open when input switch control is in alow state (e.g. value of 0). A person skilled in the art will understandthat other implementations to obtain the switch control signal arepossible. Also, one skilled in the art will understand that it is notlimited to open and closed loop, but can be a switching betweendifferent levels of feedback or even a continuously variable level offeedback. FIG. 28 shows the feedback being switched based on theenvelope compared to a reference level. As mentioned, the feedback couldbe continuously varied, for example based on the envelope voltage, orother parameters such as input power level.

FIG. 29 is an exemplary depiction of relationships between the varioussignals mentioned in previous paragraphs. Starting from the RF_(in)signal and a preset minimum level corresponding to the minimum ET supplypower level, the envelope signal, the supply power control signal andthe switch control signal are generated.

Furthermore and in order to compensate for possible mismatch of theoutput impedance of the amplifier stage between the two distinctconfigurations (feedback loop active and feedback loop not active), andthus loss of effective output power seen by the next stage, a tunablematching network can be added at the output stage of the power amplifier(e.g. FIG. 1). Same controller unit as previously mentioned can controlsuch a network as well. FIG. 20, later described in detail, shows anembodiment wherein a switchable feedback network (2100) is used within afeedback path created around a first stage amplifier (2115), which isfollowed by a tunable matching network (2120). The tunable matchingnetwork may be continuously variable or variable in discrete steps undercontrol of an input control signal (2103). Same tunable matching networkmay also be used for modifying the load lines of the amplifier stage(2115) and thus impact gain, since amplifier gain is proportional to itsload (e.g. G_(voltage)≈g_(m)×R_(Load)).

In another example, a two-stage amplification can be used wherein thefirst stage preconditions the input RF power level to the second stagesuch as to reduce switching of the second stage to the linear region ofoperation, thus enhancing overall power efficiency and linearity of theoutput stage; since minimum RF input power level to the second amplifieris increased by the first amplification stage, second amplifier willoperate more time in the compression region for an increase in overallefficiency. In this configuration, both stages can be ET amplifiers,each with its own ET power supply and each fitted with a switchablefeedback network for optimal overall performance. FIGS. 20-21 and FIG.23, later described in detail, depict such embodiments. A person skilledin the art will understand that such a configuration is not limited totwo stages and can easily be extended to multiple stages.

FIG. 20 shows an embodiment of the present disclosure where a feedbacknetwork (2100) is connected through a feedback path to an amplifierarrangement comprising a driver stage (2115) and a final stage (2125).Each of the amplifiers (2115, 2125) can be built by including a stackedarrangement of FETs in a cascode configuration as depicted by FIGS. 1-8.The amplifier arrangement of FIG. 20 further comprises an input terminal(2105) and an output terminal (2165). In other embodiments, it may bedesired that the arrangement operate in differential signal mode, inwhich case alongside the input terminal (2105) and the output terminal(2165), the amplifier arrangement would also have, at each terminal, arespective complementary signal terminal.

The feedback network (2100) is used within a feedback path to create afeedback loop around the driver stage (2115), such as when the feedbackloop is active, the output of the driver stage (2115) is taken andcombined with the input of the same driver stage (2115) after beingsubjected to the transformation defined by the feedback network (2100).Such feedback loop is active when the switch (2112) is closed, thusengaging the feedback network (2100) into creating the loop. Controlsignal to switch (2112) is provided at terminal (2102). By way ofexample and not limitation, feedback network (2100) is comprised of theswitch (2102) and RC series network (2110) in series.

As shown in FIG. 20, each of the driver stage (2115) and final stage(2125) is provided with a corresponding dynamic power source (2130) and(2140) respectively, each of them being, in turn, powered by supplyvoltages (2135) and (2145) respectively. The power sources (2130, 2140)can be variable voltage sources (e.g. a DC-DC converter) or variablecurrent sources, and are controlled via control signals fed tocorresponding input controls (2132, 2142) respectively.

A possible circuital connection between the amplifier stage (e.g. adriver stage or a final stage) and the dynamic power source is shown inFIG. 1, wherein a variable power supply provides bias power to the drainof the output transistor as well as to the gates ETG₂ and ETG₃ of thestacked transistors via a ladder resistor network. FIG. 8 shows anotherpossible configuration of the amplifier stage wherein the biasing of thegates can be done through external supplies fed to the various gates. Inboth configurations, biasing for the gate of the input transistor may bedone through ETG₁. A control signal (ctrl) to the variable power supplyis used to dynamically adjust its output power level such as the outputpower level varies as a function of time.

Going back to FIG. 20, control signals fed to inputs (2132, 2142) can beused to set corresponding amplifier stages (2115, 2125) to independentlyoperate in ET or non-ET modes. For example, in one embodiment, to set anamplifier stage to a non-ET mode, a fixed static control voltage is usedto set a fixed supply to the amplifier stage, whereas a control voltagerepresenting the envelope signal of the RF_(in) signal is fed to theamplifier stage when an ET mode of operation is desired. A person ofordinary skill in the art will understand that this flexibility ofcontrolling the power sources (2130, 2140) via control signals (2132,2142), allows for dynamic switching between the two operational modes ofa given amplifier stage (2115, 2125), given a corresponding controlsignal (2132, 2142) which dynamically switches between a static leveland one representing the envelope signal. More such embodiments tocontrol the amplifier's operation between these two modes are describedin later paragraphs. It should be noted that the bias voltage of thecascodes can also be switched between operations in ET and non-ET modes.

Furthermore and as depicted in FIG. 20, by virtue of its switchablefeedback network (2100) and the tunable matching network (2120) at itsoutput stage, the configuration of amplifier (2115) provides the addedadvantage over the configuration of amplifier (2125) of allowing furthercontrol of the amplifier's (2115) overall response based on the mode ofoperation (ET or non-ET).

As previously noted, control signals for input controls (2132, 2142) canbe generated within a transceiver unit, which typically generates themodulated RF input signal to the amplifier arrangement at input terminal(2105), and thus has full knowledge of the input data used to generatethe RF signal. As such, the transceiver unit can be fitted withdedicated circuitry and lookup tables suitable to generate the desiredcontrol signals not only for the supply voltages (e.g. gates and drainbias supplies) but also for controlling the switch unit (2112) via inputcontrol (2102) and the tunable matching network unit (2120) via inputcontrol (2103). For example, when a control signal to input (2132)dictates an ET operational mode for the amplifier unit (2115), thetransceiver unit concurrently generates a control signal (2102) to theswitch unit (2112) to open the switch and a control signal (2103) totunable matching network unit (2120) to optimize impedance matchingbetween input stage to amplifier unit (2125) and output stage ofamplifier unit (2115) when in ET mode. Alternatively, when controlsignal to input (2132) dictates a non-ET operational mode, controlsignals to close the switch unit (2112) and to set the tunable matchingnetwork unit (2120) for non-ET impedance matching are concurrentlygenerated by such transceiver unit. In this case, the feedback network(2100) and tunable matching network unit (2120) determine the responseof the amplifier. Furthermore and as previously mentioned, gate biassupplies to various transistors within the stack may additionally beadjusted, by same controller unit, to control amplifier's response ineither modes of operation.

The person skilled in the art will understand that a transceiver unit isjust one example of a controller capable of performing the task ofconfiguration control for elements (2112, 2115, 2120) of FIG. 20. Ingeneral, any controller with sufficient processing power and with accessto the RF input signal or corresponding baseband data is able to performsuch task. The person skilled in the art may find other possibleimplementations for this task, using simple logic gates and/or morecomplex arrangements including CPLDs and FPGAs.

While the control signal used to control the output level of thevariable power supply can steer a corresponding amplifier stage tooperate in a desired region, due to limitations discussed earlier whenoperating in an ET mode, exclusive operation in more efficientcompression region is not always possible as there will be instanceswhere the input RF power level is smaller than the supply power level,since latter is bounded by the minimum preset level, causing theamplifier to operate in the non-compression (linear) region.

As such, the control signal fed to input (2132) of the variable powersupply unit (2130) defines the operational strategy of the amplifierunit (2115) with respect to the input RF_(in) signal fed to input(2105). In other words, the switching of the amplifier unit (2115)between operating in the compression and linear regions is not onlyfunction of the input control (2132), but also function of input RF_(in)signal (2105). That is, when operating in the ET mode, for a given powerlevel of the RF_(in) signal (2105) at a given instance, compressionoccurs if such power is larger than the dynamic power supplied to theamplifier unit (2115), thus causing the amplifier to operate in thecompression region. Alternatively, when power level of the RF_(in)signal (2105) is below the threshold set by the variable power supply,compression does not occur and amplifier (2115) operates in the linearregion. As previously mentioned, this switching of the amplifieroperation from one region to the other is dependent on the modulationscheme used to generate the input RF signal and becomes more pronouncedin cases where modulation schemes with high peak-to-average power ratioare used.

Considering the embodiment of FIG. 20, when amplifier unit (2115) isoperating in an ET mode, a controller which at any given instant in timeis aware of both the dynamic supply power level (e.g. via thecorresponding control signal (2132)) and the RF_(in) power level beingfed to the amplifier unit (2115), can predict when switching betweenoperation in the compression region and the linear region occurs foramplifier unit (2115). Therefore, such controller can generate timelycontrol signals (2102, 2103) to dynamically configure amplifier stagevia feedback network (2100) and tunable matching network (2120) foroptimal operation, and thus reducing the undesired effects due to thechange of the region of operation of the amplifier and as described inprevious sections. In this case the switching and therefore associatedcontrols may be provided to operate at speeds equivalent (or higher) tothe modulation carrier frequency used to generate the RF_(in) signal soto be able to react quickly and therefore reduce the time in which theamplifier is not optimized (e.g. amplifier operating in linear regionand feedback network not switched in). This is in contrast to theswitching between ET and non-ET modes described previously and for whicha static control signal may be used as switching speed is not relevant.Under supervision of the same controller, adjustments to the gates biassupplies of the various transistors within the stack for controllingoutput linearity of the amplifier stage when operating in each region isalso possible (e.g. FIGS. 8, 30).

The above changes in amplifier configuration and various adjustmentsaffecting its operation may engender some undesired effects measurableat the output signal of the amplifier. In one embodiment, theseundesired effects may be further controlled by pre-distortion (e.g.phase, amplitude) of the input RF signal to the amplifier stage, in amanner to compensate for these effects. Simulation results may be usedto create lookup tables which may be subsequently used by the controllerduring operation. These lookup tables may include mapping of the variouschanges and adjustments to pre-distortion coefficients to be applied tothe input RF signal. FIG. 30 shows an exemplary system configuration forproposed embodiment, wherein a transceiver is used as main controller.

Although FIG. 20 shows a particular arrangement of the driver stage(2115), the final stage (2125) and the feedback network (2100), itshould be noted that alternative arrangements could also be implemented,as depicted by FIGS. 21-25.

In a similar manner and as depicted in FIG. 21, a feedback network(2100) can also be implemented to optimize response of the final stage(2125) when operated in the linear region. In this case the feedbacknetwork (2100) is optimized based on the electrical characteristics ofthe amplifier (2125), which may be different from the characteristics ofamplifier (2115).

FIG. 23 depicts an embodiment wherein both amplifiers (2115, 2125) arefitted each with a feedback network (2100, 2100 a) selected to optimizeresponse of each amplifier when operating in the linear region. In thiscase, feedback network (2100) is used to optimize response of amplifier(2115) and feedback network (2100 a) is used to optimize response ofamplifier (2125). Each of the feedback networks can independently beswitched in and out using the dedicated switch control signals (2102,2102 a) which control the state of the switches (2112, 2112 a). Thisconfiguration allows the flexibility to independently operate eachamplifier in ET mode or non-ET mode, as well as optimizing operation ofeach amplifier when operating in their respective regions. Tunablematching network (2120) with associated control signal (2103) are usedfor matching output stage impedance of the arrangement composed by(2115, 2100) with the input impedance of the following stage composed of(2125, 2100 a) for optimum power transfer between the two stagesirrespective of their operating regions. To be noted that in thisconfiguration the second amplifier (2125) is also fitted with a tunablematching network (2120 a) at its output. Under control of (2103 a) thisnetwork can be tuned for optimum power transfer between the arrangementcomposed of (2125, 2100 a) and the subsequent stage not shown in thefigure (e.g. antenna). Although not shown explicitly in the figure,controls (2132, 2142) may also be used to adjust various gate biases asneeded.

In yet another embodiment and as depicted by FIG. 22, a feedback network(2100) is used to create a single feedback loop around the combinationof amplifiers (2115, 2125) and tunable matching network (2120) to againoptimize overall response (e.g. linearity, phase, gain, stability) ofcorresponding arrangement when operated in the linear region.

Furthermore, although two amplifiers are currently shown in FIGS. 20-23,it is also possible to use more than two amplifiers such as in caseswhere the arrangement, for example, contains a pre-driver stage, adriver stage and a final stage.

In FIGS. 20-23, a tunable matching network (2120) is connected betweenthe driver stage (2115) and the final stage (2125). It should be notedthat the tunable matching network (2120) need not necessarily be presentonly in the arrangement as shown in these figures. As such, it ispossible that other embodiments place the tunable matching networkbefore the driver stage (2115) or after the final stage (2125) (e.g.FIG. 23). Furthermore, there may be embodiments where multiple tunablematching networks, each with dedicated control input, can be usedin-between stages, with the main goal of adaptive impedance matchingamongst stages subjected to mode/region changes and/or for modifying theload lines of the amplifier stage and thus controlling gain (e.g.G_(voltage)≈g_(m)×R_(Load)).

In the above embodiments a switch unit is used to activate orde-activate a feedback loop around an amplifier stage with the overallgoal of controlling differences in the amplifier's response functionwhen the amplifier's region of operation changes from linear tocompression. Additionally, it was noted that in a two stageconfiguration (e.g. a driver stage followed by a final stage), the firststage amplifier gain when operating in the linear region (feedbacknetwork is engaged) can be selected such as to reduce the switching ofthe final stage to the linear region, thus increasing the time the finalstage operates in the more efficient compression region.

In yet another embodiment of the present disclosure, as shown in FIG.25, the feedback network (2400) includes a variable resistor (2410)which value can be controlled using a control signal fed to the inputcontrol terminal (2404). Here, instead of having the feedback network(2400) included or excluded in the feedback path to the driver (2415) bya controlled switch unit, the variable feedback resistor's (2410) valueis controlled in order to adjust the response of the driver stage (2415)when operating in each region. For example, when operating in the linearregion, the resistance value may vary within a first range suitable fora lower gain of the amplifier stage, and when operating in thecompression region the resistance value may vary within a second rangesuitable for a higher gain of the stage. Resistance value of thisresistor may either be continuously variable or variable in discretesteps under control of (2404). This embodiment allows for all thebenefits of the prior embodiments, with the added benefit of fine tuningthe amplifier gain via incremental resistor changes. Additionally, thisembodiment allows for smooth transition between the two regions bygradually varying the resistance value (e.g. from a high value when inthe compression region to a low value when in the linear region) andthus removing possibility of glitches and other related undesiredeffects arising from an abrupt change of the feedback configuration.Finally, this feature can also be advantageous when the amplifier issubjected to different input RF modulation schemes, each requiring adifferent first stage gain in order to improve efficiency of the finalstage (so increase operation time in the compression region).

The person skilled in the art will know that he feedback function orvariable gain function can be realized in various ways. For example, thefeedback can be in the form of a shunt resistor from the source of theinput device to ground (degeneration), or a variable gain amplifiertopology, many of which are common in the industry. The feedback can beswitched, variable, or variable and switched.

It should be noted that although the inventors have discussed a“feedback network” as a means to optimize and adapt gain/response of anamplifier stage when switching between regions of operation (e.g. linearregion vs. compression region), for the sake of simplicity and not bylimitation of the embodiments, all figures show the feedback network asan RC series network with the addition, in some cases, of a switch. Aperson skilled in the art will understand that the presented embodimentsallow for various types of feedback networks, whether tunable or fixedand/or using active or passive elements, to be used, based on thedesired overall response of the corresponding amplifier stage andgoverned by known amplifier feedback design techniques. Tuning of such afeedback network is merely limited by the elements comprised in thenetwork and can be easily adapted for given the built-in intelligence inthe controller. FIG. 33 shows an embodiment of the present disclosurefor a tunable feedback network.

Furthermore, it should also be noted that although FIGS. 20-23 and FIG.24 do not show a feedback loop (e.g. open loop) when the amplifier is inET mode or when it operates within the compression region, in practicehowever, the implementation may include some active feedback componentsaround the amplifier, whether specifically dictated by designrequirements or due to parasitic effects at operating frequencies (e.g.due to corresponding circuit layout). The embodiment presented in FIG.25 provides a fixed active feedback path and the adjustable variableresistor (2410) may be used in any mode or region of operation tocontrol the response of the amplifier arrangement. FIGS. 31-32 showother possible embodiments.

In FIG. 31, the first stage arrangement of FIG. 20 is shown with theaddition of a fixed feedback loop (2113), which may be contributed toparasitic effects as discussed earlier. When the amplifier unit (2115)operates in the linear region, the feedback network (2100) is switchedin (switch (2112) close) and thus the overall feedback network aroundthe amplifier stage becomes the equivalent network comprised of the twonetworks (2100, 2113) put in parallel. Design implementation willtherefore take into account contribution of network (2113).

In FIG. 32, in addition to the fixed network (2113) of FIG. 31, anadditional network (2114) is shown. Network (2114) can be a designrequirement for the case where the amplifier unit (2115) operates in thecompression region. When operating in the compression region, the switch(2112) is closed, thus reducing feedback network (2100) to a lowresistance resistor (equivalent circuit of the closed switch). In thiscase, the effective feedback network around the amplifier unit (2115)can be approximated by the equivalent network comprised of the twonetworks (2113, 2114) in parallel. When the amplifier (2115) operates inthe linear region, the network (2100) is inserted in the feedback loopby opening the switch (2112). In this case the effective feedbacknetwork around the amplifier unit (2115) becomes the equivalent networkcomprised of the two networks (2100, 2114) in series, in parallel withthe network (2113). Here again, well known amplifier feedback designtechniques can be used to derive the component values for each of thenetworks, once the parasitic network (2113) is identified. It should benoted that in the case of the FIG. 32, for operation in the linearregion the switch (2112) needs to be open, and not close as it was thecase in all other design examples.

As previously discussed, the term “ET” mode can refer to the mode ofoperation where one or more bias voltages or bias currents are varied asa function of an envelope signal. Such mode can be used to cause theenvelope tracking amplifier to operate in a compression region therebyincreasing amplifier efficiency. Also, the term “non-ET” mode can referto the mode of operation where no bias voltages and no bias currents arevaried (e.g. as a function of an envelope signal). Such mode can be usedto cause the envelope tracking amplifier to operate in a linear region.

Going back to FIG. 1, it shows an example embodiment according to thepresent disclosure of an envelope tracking amplifier (100) capable ofadapting between ET mode and non-ET mode. The ETPS (180) of FIG. 1 isinfluenced by a control signal ctrl (190) generated externally from theenvelope tracking amplifier (100). The control signal ctrl (190)provides a time-varying envelope signal to the ETPS (180), which mayindicate a desired mode of operation (ET mode or non-ET mode). Based onthe control signal ctrl (190), the ETPS (180) provides to the stack ofFETs a corresponding power (envelope tracking/variable power supply or anon-envelope tracking/constant power supply). Although control signalctrl (190) appears to provide input only to ETPS (180), implementationscould also include related signals from control signal ctrl (190) toprovide appropriate secondary control signals to related switches andtunable elements within an envelope-tracking amplifier arrangement andto related switches and tunable elements externally connected to theenvelope tracking amplifier arrangement to appropriately configure theoverall behavior of one or more envelope-tracking amplifiers (orconfigure an envelope tracking embodiment) to operate in a desired modeof operation (ET or non-ET mode). Furthermore, although the controlsignal, as depicted in FIG. 1, is generated externally from the envelopetracking amplifier (100), other embodiments could incorporate methods orimplementations where such control signals can be generated within theenvelope tracking amplifier (100).

In one embodiment, the amplifier system would be switched from ET modeto non-ET mode of operation when the input and thus output power leveldrops to a point that the power consumption in the ETPS is more than thepower it saves. As an example, the amplifier may operate in ET mode fromthe maximum average output power down to the maximum average power—10dB. At that time the ETPS would be switched off, bypassed, or switchedto an average power tracking mode, (average power tracking mode is onewhere a DC-DC converter slowly follows the average power of theamplifier and an analog error amp would not be required). The non-ETmode would be used at this power and all lower power levels. The exampleof Pmax−10 dB is an example. The actual value depends on the systemoptimization, including amplifier efficiency with and without ET and thepower consumption of the ETPS.

A transceiver can be such an example of a source that could be used toprovide control signals to the envelope tracking amplifier (100)indicating a desired mode of operation and thereby configure theenvelope tracking amplifier (100) to adapt to the desired mode ofoperation. The transceiver used to provide an input signal to theenvelope tracking amplifier (100) could know a desired mode of operationfor a particular input signal being provided. Thus an embodiment couldbe imagined where the transceiver also provides control signals to theETPS and/or related switches and tunable elements of an embodiment toconfigure the embodiment to operate accordingly.

FIG. 34 shows an example embodiment according to the present disclosurecomprising an envelope tracking amplifier (3400) (e.g. the envelopetracking amplifier (100) shown in FIG. 1), an envelope detector (3410)and a control unit (3420). The envelope detector (3410) can comprise theimplementation shown in FIG. 2 or can be implemented in any manner thatis within the capability of a person skilled in the art. An input signal(e.g. an RF signal) can be fed to both to the input port of the envelopetracking amplifier (3400) as well as the envelope detector (3410). Theenvelope signal from the envelope detector (3410) can be fed to thecontrol unit (3420). The control unit (3420) can produce the controlsignal (3490) based on the envelope signal from the envelope detector(3410). As discussed above, the control signal ctrl (190) of FIG. 1 isused to indicate to the ETPS (180) of FIG. 1 what type of power(variable supply power or constant supply power) to provide to the stackof FETs given a desired mode of operation (envelope tracking ornon-envelope tracking). The control signal (3490) of FIG. 34, generatedby the control unit (3420) can be an example of an external generator ofthe control signal ctrl (190) of FIG. 1. Additionally, a basebandsignal, such as an in-phase and quadrature phase Cartesianrepresentation, can also be used to create the envelope signal. In analternative embodiment, the envelope signal is fed directly to theenvelope tracking amplifier (3400), in particular to the ETPS (180) andused as the control signal (3490).

Furthermore, the control unit (3420) can also provide one or moresecondary control signals (3430) to other components (e.g. aconfiguration arrangement comprising switches and/or tunable elementssuch as tunable resistors and tunable capacitors) within the envelopetracking amplifier (3400). The one or more secondary control signals(3430) can configure one or more switches and/or one or more tunablecomponents within the envelope tracking amplifier (3400) described belowsuch that the one or more switches and/or one or more tunable componentsare adapted to operate according to the desired mode of operation.

As stated above, other devices external to the envelope trackingamplifier can provide one or more control signals to the ETPS (180)and/or related switches and tunable elements. For example, a transceivercan be used to provide an input signal to the envelope trackingamplifier. Since the transceiver would know what is being provided tothe envelope tracking amplifier, the transceiver could also provide anindication (either through an envelope signal and/or control signal) tothe ETPS (180) and/or related switches and tunable elements to configurethe envelope tracking amplifier to operate in a desired mode ofoperation (ET mode or non-ET mode) adapted for the input signalprovided.

The envelope tracking amplifier (100, 800) shown in FIGS. 1 and 8 canboth be connected to additional circuitry that is configured to enablean amplifier arrangement comprising the envelope tracking amplifier toadapt between operation in an ET mode or in a non-ET mode. By way ofexample, and not of limitation, the additional circuitry can compriseone or more switches, one or more passive elements (e.g. resistors orcapacitors), one or more active elements (e.g. one or more FETs oramplifiers), or some combination thereof. Furthermore, secondary controlsignals (3430) discussed above, different from the control signal(3490), can be generated to configure other elements besides the ETPS(180) influencing, thereby assisting the envelope tracking amplifier toadapt between operation in the ET mode or in the non-ET mode. Numerousembodiments comprising an envelope tracking amplifier (such as theenvelope tracking amplifiers (100, 800) shown in FIG. 1 or 8) connectedto additional circuitry that provides additional functionality arepresented below.

As stated above, it is desirable to have an envelope tracking amplifierbe configurable to operate between operating in ET and non-ET mode. Insuch situations the envelope tracking amplifier (such as the envelopetracking amplifier (100) of FIG. 1) can be configured to adapt betweenET mode and non-ET mode by adjusting the dynamic bias voltages appliedto the gate and drain of the stack of FETs (ET_(RD3) and ET_(DR)). Forexample, for non-ET mode, the envelope tracking amplifier (100) of FIG.1 can have the second dynamic bias voltage ET_(DR) be held at a fixedvalue. Furthermore, fixed gate bias voltages ET_(G1), ET_(G2) andET_(G3) are also provided to the gate bias terminals. It should be notedthat selection of dynamic bias voltages to operate an envelope trackingamplifier in the non-ET mode described in this paragraph may also beapplied to envelope tracking amplifiers comprising a number of stackedtransistors other than three. It should also be noted that embodiments,within the scope of the present disclosure, could be implemented wherethe DC gate bias voltage stays the same or changes when the mode of theenvelope tracking amplifier is switched. Furthermore, the decision tochange or maintain the DC gate bias voltage can be made in conjunctionwith or separate from the state of a tunable matching network based onan indicated mode of operation. A person skilled in the art will notrequire further explanation or diagrams to understand such embodiments.

In some other embodiments switching between other modes, not just ET andnon-ET may be desired. This may include such modes as polar, ET,envelope following, and fixed supply.

FIGS. 35-37 show different embodiments according to the presentdisclosure used to configure an envelope tracking amplifier (3500)between operation in ET and non-ET mode. FIG. 35 utilizes an inputtunable matching network (3510) and an output tunable matching network(3520). The input tunable matching network (3510) can be tuned toprovide impedance matching between an input terminal (3505) and an inputof the envelope tracking amplifier (3500). The output tunable matchingnetwork (3520) can be tuned to provide impedance matching between anoutput terminal (3530) and an output of the envelope tracking amplifier(3500). Either or both of the tunable matching networks can be tunedappropriately, based on an envelope signal, depending on whether the ETmode or the non-ET mode of operation is desired for the envelopetracking amplifier (3500) as each mode of operation could desire adifferent type of impedance matching. This is the case as it is possiblethat the network, between ET mode and non-ET mode, each have a differentoptimal match.

FIGS. 36 and 37 utilize a resistor-capacitor feedback loop (3540) toconfigure the envelope tracking amplifier (3500) between operation in ETand non-ET mode. In FIG. 36, a resistor-capacitor feedback loop (3540)is shown whereby a feedback switch (3545) controls when theresistor-capacitor feedback loop (3540) is used. Depending on thedesired mode of operation, the feedback switch (3545) can be open orclosed to disable or enable, respectively, the use of theresistor-capacitor feedback loop (3540). The resistor-capacitor feedbackloop (3540) can be used to adjust the gain of the envelope trackingamplifier (3500) based on a desired mode of operation

Alternatively, FIG. 37 shows another resistor-capacitor feedback loop(3540) except that in this embodiment the resistor and capacitorelements are tunable. Depending on the desired mode of operation, theresistor and capacitor elements of the resistor-capacitor feedback loop(3540) can be tuned to configure the envelope tracking amplifier (3500)to operate in ET or non-ET mode.

Generally speaking, embodiments comprising a plurality of amplifiersthat are operatively connected in cascade, where one or more of theamplifiers are envelope tracking amplifiers, configured to switchbetween the ET mode and the non-ET mode, can be accommodated by usingone or more switches to selectively include or bypass one or moreamplifiers from among the plurality of amplifiers. When operating in theET mode, appropriate operation of the switches can increase the totalnumber of amplifiers present in a signal amplification path. Conversely,when operating in the non-ET mode, appropriate operation of the switchescan decrease the total number of amplifiers present in the signalamplification path. The term “signal amplification path” can refer to apath which an input signal flows through while being amplified bysuccessive amplifiers operating in cascade. Numerous embodiments thatoperate by using switches to selectively include or omit one or moreamplifiers in the signal amplification path are possible, two of whichwill be described below. Implementations of such embodiments arealternative ways to configure a particular embodiment to operateaccording to a desired mode of operation (ET or non-ET mode).

FIG. 38 shows an embodiment according to the present disclosure that canbe used to configure a plurality of amplifiers to adapt betweenoperating in ET and non-ET mode. The embodiment of FIG. 38 comprises aninput terminal (3810), a first amplifier (3820), a first switch (3830),a second amplifier (3850), a through circuit (3840), a third amplifier(3860), a second switch (3835) and an output terminal (3870). An inputport can comprise the input terminal (3810) and ground, while an outputport can comprise the output terminal (3870) and ground. In theembodiment shown in FIG. 38, one or more of the amplifiers (3820, 3850,3860) can be an envelope tracking amplifier such as the envelopetracking amplifier (100) shown in FIG. 1 or the envelope trackingamplifiers 800, 800A shown in FIG. 8 and FIG. 8A. The first switch(3830) can be operated to select either the second amplifier (3850) orthe through circuit (3840). The second switch (3835) would be enabled atthe same time to follow the selection of the first switch (3830) so thatone path is chosen while the other path is completely removed. Foroperation in the non-ET mode, the first and second switches (3830, 3835)can be operated to select the through circuit (3840), allowing signalflow from the input terminal (3810) to the output terminal (3870) tobypass the second amplifier (3850). For operation in the ET mode where ahigher gain may be required to keep the amp in compression and/orcompensate for the reduced gain when in compression, the first andsecond switches (3830, 3835, respectively) can be operated to select thesecond amplifier (3850), thereby including all three amplifiers (3820,3850, 3860) in a signal amplification path that begins at the inputterminal (3810) and ends at the output terminal (3870) where such signalamplification path is configured to operate for ET mode.

Alternatively, a second through path can be added to the embodimentshown in FIG. 38 to allow an input signal to be routed through the firstamplifier (3820) or bypass the first amplifier (3820) in addition tofeatures already described that allow inclusion or bypassing of thesecond amplifier (3850) as described above. In other embodiments, thefirst and second switches (3830, 3835) and the through path (3840) areapplied only to the first amplifier (3820) such that only the firstamplifier (3820) can be included or bypassed, depending on switchoperation. Additional embodiments include a switch and a through paththat are connected to the third amplifier (3860) in a similar mannerthat allows the third amplifier (3860) to be bypassed depending on themode of operation, either alone or in combination with featurespreviously described that allow inclusion of or bypassing of the firstamplifier (3820) and the second amplifier (3850). Alternativeembodiments comprise two, four, or more amplifiers. Such alternativeembodiments may be configured to allow including or bypassing one ormore of the amplifiers depending on operation of one or morecorresponding switches. A person skilled in the art will not requirefurther explanation or diagrams to understand such embodiments.

FIG. 39 shows another embodiment that can be used to configure anoperation of an amplifier between ET mode and non-ET mode. Inparticular, FIG. 39 shows an input terminal (3910), a first amplifier(3920), a second amplifier (3940), a path with a switch (3930), and anoutput terminal (3950). Either or both amplifiers (3920, 3940) can beenvelope tracking amplifiers. For the ET mode, the switch (3930) can beopened to include the second amplifier (3940) in a signal amplificationpath between the input terminal (3910) and the output terminal (3950).For the non-ET mode, the switch (3930) can be closed to omit the secondamplifier (3940) from the signal amplification path between the inputterminal (3910) and the output terminal (3950). In addition to theaforementioned switch operation, for the non-ET mode, the secondamplifier (3940) can be disabled (e.g. by switching off its power supplyor by adjusting bias circuits to put the circuit in a low power standbymode).

Furthermore, FIG. 40 shows an alternative embodiment to the embodimentseen in FIG. 39 comprising input terminal (4010), an output terminal(4050), a first switch (4030) and a second switch (4035) can be used toselect between two possible paths wherein the two possible pathscomprise one or more amplifiers (4040). The plurality amplifiers (4040)can be envelope tracking amplifiers. For ET mode (including modes suchas envelope following and polar) or non-ET mode (e.g. linear operation),the first and second switches (4030, 4035) would be used to select oneof the two paths, where one path could be configured for ET mode and theother path configured for non-ET mode by tuning the parameters of theone or more amplifiers belonging to a particular path. Selection of aparticular path would configure the overall embodiment according to thedesired mode of operation (ET or non-ET mode). In some embodiments thisselection can be made based on certain operating parameters, such asinput and/or desired output power level. For example, the ET path can beused at high output power levels (Pmax to Pmax−10 dB, for example), andthe linear or non-ET path can be used at the lower power levels.Additionally, an input tunable matching network and/or an output tunablematching network (not shown) could be provided for one or both possiblepaths shown in FIG. 40. Such arrangements could be implemented in asimilar manner as shown in the embodiment of FIG. 35.

Returning to FIG. 39, the path with the switch (3930) can be configuredto pass a signal unaltered when the switch (3930) is closed, enabling aninput signal (e.g. an RF signal) applied to the input terminal (3910) tobe amplified only by the first amplifier (3920) when the switch (3930)is closed and the second amplifier (3940) is disabled. Alternatively,the path with the switch (3930) can be placed parallel to the firstamplifier (3920) in order to selectively utilize or bypass the firstamplifier (3920) for operation in the ET mode or the non-ET mode,respectively, together with appropriately enabling or disabling thefirst amplifier (3920) as previously discussed with respect to thesecond amplifier (3940). Other embodiments may comprise three or moreamplifiers with one or more paths with switches to selectively includeor omit, from a signal amplification path, one or more amplifiers incorrespondence of the one or more paths with switches depending onwhether the ET mode or the non-ET mode of operation is desired. Such anexample of other embodiments can be seen in FIG. 40.

When switching between ET mode and the non-ET mode, a resistance valueand/or a capacitance value present at a gate of any FET in a stack ofFETs used in constructing an envelope tracking amplifier, except a firstFET (e.g. the first FET (115) in FIG. 1) to which an input signal (e.g.an RF signal) is applied, can be configured as a function of a desiredmode of operation (ET mode or non-ET mode). Numerous embodiments thatoperate by adjusting a resistance value and/or a capacitance valuepresent at a gate of any FET in a stack of FETs used in constructing anenvelope tracking amplifier are possible, two of which are discussedbelow. Also, as previously mentioned, the concept of switching betweenET mode and non-ET mode can also be extended to other modes, such aspolar, envelope following or other.

FIG. 41 shows an embodiment according to the present disclosure of aswitchable gate bias network that can be connected, for example, to thesecond FET (120) or the third FET (155) shown in the embodiment ofFIG. 1. In the embodiment shown in FIG. 41, the switchable gate biasnetwork comprises a gate resistor switch (4110), a gate resistor (4120),a gate capacitor (4130), and a gate capacitor switch (4140). Operationof the gate resistor switch (4110) can effectively include or omit thegate resistor (4120) in a path between the second gate bias terminal(135) and the gate of the second FET (120) of FIG. 1. Similarly,operation of the gate capacitor switch (4140) can effectively include oromit the gate capacitor (4130) in a path between the gate of the secondFET (120) of FIG. 1 and ground. Operation of the gate resistor switch(4110) and the gate capacitor switch (4140) may be determined by whetherthe ET mode or the non-ET mode of operation of the envelope trackingamplifier (100) of FIG. 1, for example, is desired.

For the ET mode operation, as seen in FIG. 41, the gate resistor switch(4110) can be closed, thereby providing a low resistance path thatbypasses the gate resistor (4120), effectively removing the gateresistor (4120) from the path between the second gate bias terminal(135) and the gate of the second FET (120) of FIG. 1. For the non-ETmode operation, the gate resistor switch (4110) can be opened,effectively including the gate resistor (4120) in the path between thegate bias terminal (135) and the gate of the second FET (120) of FIG. 1.For the non-ET mode operation, the gate capacitor switch (4140) can beclosed, effectively including the gate capacitor (4130) in the pathbetween the gate of the second FET (120) and ground of FIG. 1. For theET mode operation, the gate capacitor switch (4140) can be opened,effectively removing the gate capacitor (4130) from the path between thegate of the second FET (120) and ground of FIG. 1. The above descriptionprovides a number of ways to provide a particular bias to the gate ofthe second FET (120) for the purpose of configuring the particular FETso as to have the overall envelope-tracking amplifier operate in ET ornon-ET mode. Similar arrangements and behaviors for the gate resistorswitch and the gate capacitor switch can be included for all FETs exceptfor the first FET, which is biased in a different way as describedlater.

With reference to the embodiment shown in FIG. 41, either or both of thegate resistor switch (4110) and the gate capacitor switch (4140) can bea stacked switch (e.g. a switch comprising stacked transistors) in orderto allow power handling capability greater than a power handlingcapability of a switch comprising a single transistor because a voltagepresent at the gate of the second FET (120) or a higher FET of FIG. 1may be sufficiently high that a switch comprising a single transistorwould not be appropriate. Other alternative embodiments that may includethe gate resistor switch (4110) and the gate capacitor switch (4140) canimplement those switches as stacked switches for similar reasons.Reference can be made for example to U.S. Pat. No. 7,910,993 B2, issuedon Mar. 22, 2011, entitled “Method and Apparatus for Use in ImprovingLinearity of MOSFETs Using an Accumulated Charge Sink”, and U.S. Pat.No. 8,129,787 B2, issued on Mar. 6, 2012, entitled “Method and Apparatusfor Use in Improving Linearity of MOSFETs Using an Accumulated ChargeSink”, both of which are incorporated herein by reference in theirentirety.

Another alternative can be seen in FIG. 42 where an additional resistor(4225) is included to the embodiment seen in FIG. 41. The additionalresistor (4225) can be tunable as well. The purpose of resistor (4225)is to ensure that if gate resistor switch (4210) is closed (therebybypassing the gate resistor (4220)), the embodiment as seen in FIG. 42will still provide a resistance (through the additional resistor (4225))at the gate of the FET (120) of FIG. 1. In the event that the gateresistor switch (4210) is open, the additional resistor (4225) can betuned to have a 0 value thereby producing an effectively similararrangement as seen in FIG. 41.

Furthermore, FIG. 43 provides another alternative where an additionalcapacitor (4335), which can also be tunable, is provided. Similar to theadditional resistor (4225) in FIG. 42, the additional capacitor (4335)seen in FIG. 43 can be used to ensure that there will always be acapacitance available even if the gate capacitor switch (4340) is open.Further details regarding tunable reactive elements, including tunablecapacitors and tunable inductors, may be found, for example, inInternational Application No. PCT/US2009/001358, entitled “Method andApparatus for Use in Digitally Tuning a Capacitor in an IntegratedCircuit Device,” filed on Mar. 2, 2009, and in U.S. patent applicationSer. No. 13/595,893 entitled “Method and Apparatus for Use in TuningReactance in an Integrated Circuit Device”, filed on Aug. 27, 2012, bothincorporated herein by reference in their entirety.

FIG. 44 shows an embodiment according to the present disclosure of atunable gate bias network that can be connected to the second FET (120)or the third FET (155) shown in FIG. 1. This embodiment, as seen in FIG.44, is an alternative where switches and accompanying passive elements(gate resistor and/or capacitor) can be replaced with tunable elementsthat have values that can be controlled. In the embodiment shown in FIG.44, the tunable gate bias network comprises a tunable gate resistor(4420) connected between the second gate bias terminal (135) and thegate of the second FET (120) in addition to a tunable gate capacitor(4430) connected between the gate of the second FET (120) of FIG. 1 andground or other suitable reference voltage. For the ET mode operation,the tunable gate resistor (4420) can be set to a low value, whereas foroperation in the non-ET mode, the tunable gate resistor (4420) can beset to a high value. For the non-ET mode operation, the tunable gatecapacitor (4430) can be set to a high value, whereas for operation inthe ET mode, the tunable gate capacitor (4430) can be set to a low value(e.g. corresponding to a high signal impedance, where the term “signalimpedance” can refer to an impedance presented to a time varyingsignal). These tunable gate resistors and capacitors can be used toalternatively bias a FET to configure the envelope tracking amplifier,where the configuring of the envelope tracking amplifier is thereby ableto adapt its operation as the mode of operation of the embodimentchanges between ET and non ET mode.

Alternately, the embodiments shown in FIGS. 41, 42, 43 and 44 can becombined in various ways to create other embodiments. By way of example,and not of limitation, the gate resistor switch (4110) of FIG. 41 can beadded to the embodiment shown in FIG. 44, connected in a manner similarto the embodiment shown in FIG. 41. Alternatively, the tunable gatecapacitor switch (4140) of FIG. 41 can be added to the embodiment shownin FIG. 44. Similar alteration or replacement of both the tunable gateresistor (4420) and the tunable gate capacitor (4430) can result in yetother embodiments.

FIG. 45 shows an embodiment according to the present disclosurecomprising the tunable gate resistor (4520), the gate resistor switch(4510), the tunable gate capacitor (4530), and the gate capacitor switch(4540). A person skilled in the art will not require further explanationor diagrams to understand such embodiments as presented in the precedingtwo paragraphs.

The embodiment shown in FIGS. 44 and 45, as well as alternatives thathave been explained above but not shown in figures, may also be appliedto the third FET (155) in FIG. 1 or 8 as well as any FET among stackedFETs used to build an envelope tracking amplifier except for a first FET(e.g. the first FET (115) in FIG. 1) to which an input signal (e.g. anRF signal) is applied. Either or both of the gate resistor switch (4510)and the gate capacitor switch (4540) of FIG. 45, for example, can be astacked switch in order to allow power handling capability greater thanthe power handling capability of a switch comprising a single transistorbecause a voltage present at the gate of the second FET (120) or ahigher FET may be sufficiently high that a switch comprising a singletransistor would not be appropriate.

FIG. 46 shows an embodiment according to the present disclosure of aswitchable gate network that can be connected the first FET (e.g. thefirst FET (115) in FIG. 1) to which an input signal (e.g. an RF signal,RF_(IN)) is applied. The embodiment shown in FIG. 46 comprises a gateresistor (4620) similar to the gate resistor (4120) shown in FIG. 41 anda gate resistor switch (4610) similar to the gate resistor switch (4110)shown in FIG. 41 that can be connected in a path between the inputsignal and a gate of the first FET to which the input signal is applied(110), while omitting a gate capacitor similar to the gate capacitor(4130) and a gate switch similar to the gate switch (4140) of FIG. 41.In the embodiments where the gate resistor (4620) and the gate resistorswitch (4610) are applied to FETs other than a first FET (e.g. the firstFET (115) in FIG. 1 or FIG. 34) to which an input signal (e.g. an RFsignal) is applied, the gate resistor switch (4610) can be a stackedswitch (e.g. a switch comprising stacked transistors) in order to allowpower handling capability greater than a power handling capability of aswitch comprising a single transistor because a voltage present at thegate of the second FET (120) or a higher FET may be sufficiently highthat a switch comprising a single transistor would not be appropriate.Other alternative embodiments that include the gate resistor switch(4610) can implement the gate resistor switch (4610) as a stacked switchfor similar reasons.

FIG. 47 shows an embodiment according to the present disclosure of atunable gate network that can be connected to the first FET (e.g. thefirst FET (115) in FIGS. 1, 3, 4, 6 and 8) to which an input signal(e.g. an RF signal) is applied. The tunable gate network can comprise atunable gate resistor (4720) that can be connected in a path between theinput signal and a gate of the first FET to which the input signal isapplied (110), while omitting a tunable gate capacitor similar to thetunable gate capacitor (4530) of FIG. 45. For the ET mode operation, thetunable gate resistor (4720) of FIG. 47 can be set to a low value,whereas for operation in the non-ET mode, the tunable gate resistor(4720) of FIG. 47 can be set to a high value.

Alternatively, the gate resistor switch (4610) of the embodiment shownin FIG. 46 can be added to the embodiment shown in FIG. 47 and connectedin a manner similar to the embodiment shown in FIG. 46. FIG. 48 shows anembodiment according to the present disclosure comprising the gateresistor switch (4810) and the tunable gate resistor (4820). In theprevious embodiments the gate resistor and the gate resistor switch wereapplied to FETs other than a first FET (e.g. the first FET (115) in FIG.1). FIG. 48 shows the gate resistor (4820) and the gate resistor switch(4810) applied to the first FET (e.g. the first FET (115) in FIG. 1) towhich an input signal (e.g. an RF signal) is applied. The gate resistorswitch (4810) can be a stacked switch (e.g. a switch comprising stackedtransistors) in order to allow voltage handling capability greater thanthe voltage handling capability of a switch comprising a singletransistor because a voltage present at the gate of the second FET(120), for example of FIG. 1, or a higher FET may be sufficiently highthat a switch comprising a single transistor would not be appropriate. Aperson skilled in the art will not require further diagrams orexplanation to understand the embodiments presented in FIG. 46-48, andwill also understand the advantage the embodiment of FIG. 47 has overthe other two, mainly due to the practicality of the implementation.

Generally speaking, when switching between the ET mode and the non-ETmode, an effective number of FETs in a stack of FETs used to constructan envelope tracking amplifier can be configured based on the selectedmode of operation. By way of example, and not of limitation, if the ETmode of operation is desired and higher amplification is needed (e.g. ahigher output power from the variable power supply across the stack ofFETs), an effective number of FETs in the stack of FETs used toconstruct an envelope tracking amplifier can be increased. Conversely,if the non-ET mode of operation is desired, the effective number of FETsin the stack of FETs used to construct an envelope tracking amplifiercan be decreased. Selection of a desired number of FETs to be active canbe provided based on a particular biasing of individual FETs of thestack of FETs. Numerous embodiments that operate by changing theeffective number of FETs in the stack of FETs used to construct theenvelope tracking amplifier are possible, two of which are presented inthe following paragraphs.

FIG. 49 shows an embodiment according to the present disclosure of analternative biasing arrangement for the third FET (155) as shown inFIG. 1. In the embodiment shown in FIG. 49, an upper terminal of thethird resistor (175) is connected to a supply switch (4920). The supplyswitch (4920) can be operated to connect the upper terminal of the thirdresistor (175) to either the ETPS (180) or to a fixed DC supply (4930),both of which can be connected to draw power from a voltage sourceV_(DD) (185, 4910). If the ET mode of operation is desired, the upperterminal of the third resistor (175) can be connected to the ETPS (180).If the non-ET mode of operation is desired, the upper terminal of thethird resistor (175) can be connected to the fixed DC supply (4930),which supplies a high DC bias voltage (constant power supply) to thegate of the third FET (155) that can bias the third FET (155) to operatein the triode region. Operation of the third FET (155) results in thethird FET acting as a resistor rather than an amplifier. Additionally,fixed power is supplied to the drain of the stack of three FETs innon-ET mode. This can be achieved either by providing a directconnection from the DC supply (4930) to the stack of three FETs.Alternatively, a bypass circuit (4940) can be implemented with the ETPS(180) such that a bypass mode can be enabled allowing the voltage supplyV_(DD) (185) to be supplied to the stack of three FETs effectivelyproviding a constant power for non-ET mode and removing the ETPS (180)from the arrangement. FIG. 49 thus presents two distinct embodiments ofthe present disclosure. First, a method to switch the device (155) totriode region of operation and thus to effectively remove it from theamplification stage. Second, a method to switch between ET mode andnon-ET mode by switching the path to the gate of the cascode.

Biasing the third FET (155) to operate in the triode region (and thushaving the third FET (155) act as a resistor rather than an amplifier)reduces the effective number of FETs in the stack of FETs used toconstruct the envelope tracking amplifier (100) of FIG. 1. In general,an n-channel FET with an applied gate to source voltage that is higherthan a drain to source voltage of the n-channel FET by an amount greaterthan or equal to a threshold voltage of the n-channel FET can functionas a resistor (triode) with a value that is a function of the appliedgate to source voltage.

Modifications similar to the embodiment shown in FIG. 49 can also bemade, for example, to the second FET (120) of FIG. 1 as well as any FETin a stack that is used to construct an envelope tracking amplifier,except for a first FET (e.g. the first FET (115) in FIG. 1) to which aninput signal (e.g. an RF signal) is applied. The embodiment shown inFIG. 49 can also be applied to the envelope tracking amplifier (800)shown in FIG. 8 by omitting the third resistor (175) of FIG. 1 andconfiguring the arrangement such that the switch (4920) of FIG. 49selects, as a bias voltage to be applied to the third gate bias terminal(145), between a high bias voltage (e.g. supplied by the fixed DC supply(4930)) that can bias the third FET (155) to operate in the trioderegion and a dynamic bias voltage that is supplied either by the ETPS(180) of FIG. 1 or a separate controller (not shown).

FIG. 50 shows an embodiment according to the present disclosure of aswitchable biasing arrangement similar to the embodiment shown in FIG.49 applied to the third FET (155) that is applied instead to the secondFET (120). A supply switch (5030) can be operated to connect the secondgate bias terminal (135) to an ET mode select terminal (5010) thatfurther connects to the second resistor (140) of the bias network shownin FIG. 1 for the ET mode. Alternatively, for the non-ET mode, thesupply switch (5030) can be operated to connect the gate bias terminal(135) to a high bias voltage terminal (5020), where such terminal (5020)is at a fixed bias voltage (e.g. supplied by a fixed voltage source)that when applied to the gate of the second FET (120) is adapted to biasthe second FET (120) in the triode region, thus causing the second FET(120) to function as a resistor instead of an amplifier. Similar to thediscussion of the embodiment shown in FIG. 49, biasing the second FET(120) to function as a resistor instead of an amplifier reduces theeffective number of FETs in the stack of FETs used to construct theenvelope tracking amplifier (100) of FIG. 1. Alternatively, theembodiment shown in FIG. 50 can also be used in conjunction with theenvelope tracking amplifier (800) shown in FIG. 8 by omitting the secondresistor (1840) of FIG. 50 and configuring the arrangement such that thesupply switch (5030) selects, as a bias voltage to be applied to thesecond gate bias terminal (135), between a high bias voltage that canbias the second FET (120) to operate in the triode region and a dynamicbias voltage that is supplied either by the ETPS (180) of FIG. 1 or aseparate controller (not shown).

With the above two embodiments, biasing a gate voltage of the FET isused to reduce the stack height. Alternatively, embodiments could beprovided where amplifier arrangements of different stack heights arechosen directly. For example, FIG. 51 shows an embodiment according tothe present disclosure of an amplifier arrangement comprising a firststack (5130) comprising three FETs, a second stack (5140) comprising twoFETs, a stack switch (5125) that can be operated to physically selectone of the two stacks (5130, 5140), an inductor (5120), and a ETPS(5110) that is connected to a voltage supply V_(DD), where the inductorserves as an RF choke and is placed in a path between the ETPS (5110)and whichever stack is selected. For the ET mode, the stack switch(5125) can be operated to select the first stack (5130), because the ETmode may require a higher DC voltage across the stack of FETs than thenon-ET mode. For the non-ET mode, the stack switch (5125) can beoperated to select the second stack (5140). In some embodiments, thefirst stack (5130) further comprises elements (e.g. as describedpreviously) appropriate to the envelope tracking amplifier (100) shownin FIG. 1, the envelope tracking amplifier (800) shown in FIG. 8, orother envelope tracking amplifiers that comprise stacked transistors.Alternatively, the first stack (5130) may comprise four or moretransistors, while the second stack (5140) can comprise any number oftransistors that is fewer than a number of transistors in the firststack (5130). By way of further example, and not of limitation, thefirst stack (5130) may comprise two transistors, while the second stack(5140) can be reduced to a single transistor (e.g. no longer a stack).

As seen in FIG. 51, both the first stack (5130) and the second stack(5140) utilize one tunable matching network (1950) prior to an output ofthe amplifier arrangement. Although use of a single shared tunablematching network (1950) can save space during implementation, thisembodiment may make the tunable matching network more challenging. Thisis because the choke (5120) would be common to both stacks and possiblynot optimized for either. As a result, the tunable matching network(1950) may have to cover a wider tuning range.

FIG. 52 shows an embodiment similar to FIG. 51 except that the stackswitch (5125) of FIG. 51 is now directly connected to the ETPS (5110) ofFIG. 51. The inductor (5220) is no longer in direct connection with theETPS (5210) but rather is part of the first stack and second stack ofFETs (5230, 5240). The re-arrangement of the inductor (5120; 5220) andthe stack switch (5125; 5225) influences matching for the embodimentseen in FIGS. 51 and 52. For example, as stated above in FIG. 51, giventhe location of the inductor (5120) and the stack switch (5125), ashared matching can be provided for the first stack (5130) and thesecond stack (5140). However, as seen in FIG. 52, because the stackswitch (5225) and the inductor (5220) is now swapped with respect to therelationship seen in FIG. 51, the first stack (5230) and the secondstack (5240) may have separate tunable matching networks (5250, 5255).

As discussed above in FIG. 51, the first stack (5130) and the secondstack (5140) may each desire a different output match. However, theembodiment uses a single sharable tunable matching network (1950) whichmay not be able to provide a desired matching for both stacks. On theother hand, the embodiment in FIG. 52 allows for the use of separatetunable matching networks (5250, 5255) for the first stack (5230) andthe second stack (5240). Although such an embodiment could use morespace during implementation compared to the embodiment of FIG. 51, theembodiment of FIG. 52 would allow a desired matching to be provided toboth the first stack (5230) and the second stack (5240). An ability toprovide the desired matching to both the first stack (5230) and thesecond stack (5240) is a further advantage the embodiment of FIG. 52 hasover the embodiment of FIG. 51. However, FIG. 52 has a lot morecomplexity and thus cost. These factors need to be considered in theselection of the implementation strategy.

Given that the embodiment of FIG. 52 has two tunable matching networks(5250, 5255) for each of the two stacks (5230, 5240), an output switch(5260) has been added to select an appropriate output based on whichstack the stack switch (5225) selects. The selected output by the outputswitch (5260) would be provided to a load (e.g. an antenna) or anyadditional circuitry to which the embodiment of FIG. 52 may be connectedto.

For all of the embodiments previously discussed in the presentdisclosure in relation to switching an amplifier operation mode betweenET and non-ET, control of switches and/or tuning of tunable elements canbe performed by control signals that are provided by a transceiver, amicroprocessor (e.g. a control unit of a cell phone or wireless device),a control circuit corresponding to any amplifier within a givenembodiment, or some other unit that is configured to provide appropriatecontrol signals, whether implemented in hardware (e.g. simple/complexdigital logic, analog), software and/or a combination thereof. Any andall parts of these various embodiments can be monolithically integratedfor better overall performance as well as reduced manufacturing cost,assembly cost, testing cost and form factor.

Going back to FIG. 1, a person skilled in the art will recognize thatdue to the high output power requirement of a cascode amplifier stage,the drain voltage supplied to transistor (155) should be of high currentcapability, whereas corresponding gate bias voltages (i.e. ET_(G1),ET_(G2), ET_(G3)) need not. In a practical sense, this high currentrequirement for the drain voltage imposes close proximity of thecorresponding generation circuitry to the cascode stage. In mostembodiments generation of the drain voltage is performed within theETPS.

Furthermore and as discussed in prior embodiments, in order to optimizeoperation (e.g. linearity, efficiency, ACLR) of the amplifier (100) inthe envelope tracking mode, each of the bias voltages ET_(G1), ET_(G2),ET_(G3) can independently be scaled, amplitude shifted, phase shifted,inverted, and/or subject to any mathematical operation (e.g. implementedby an op-amp circuit or lookup table) with relation to the bias voltagesupplied to the inductor (170) prior to being applied to gate bias nodes(110, 135, 145). In some embodiments, the bias voltage ET_(G1) may beheld fixed while the other two bias voltages ET_(G2) and ET_(G3) vary asa function of the control voltage connected to the input terminal (190)of the ETPS (180), but with differing gains and/or phases. In yetanother embodiment, ET_(G3) may be set to a high voltage to puttransistor (155) strongly in the triode region when the envelope voltageon its drain (through inductor 170) goes very low and thus removingtransistor (155) from the cascode configuration, while decreasingET_(G2) to follow the envelope and maintain the cascode effect. Thesetechniques can be applied to any or all of the gates in a stack and thestack can be anywhere from a stack of 1 to a stack of n (n>1, e.g. n=3,4, 7, . . . ).

This added flexibility of independently and dynamically controlling thevarious gate bias voltages provides for better control of the responseof the ET amplifier as compared to the traditional ET implementation,wherein only the drain voltage is controlled using an envelope signal.For example, knowing the operational characteristics of the ET amplifierwith respect to its drain input voltage, one can further optimize usingany one or combination of the controlling gate biases and create lookuptables to provide corrections to the gate biases based on the inputvoltage to the drain. Corrections can be made to optimize response ofthe ET amplifier for one or multiple of linearity, efficiency, outputpower and adjacent channel leakage ratio (ACLR) and using variousstrategies (e.g. keep one gate constant and correct for other two).These lookup tables can subsequently be used by some circuitry (e.g.waveform generation) to generate corrections during operation (e.g.increase output power request by a base station). Although these typesof corrections can be completely predicted by the drain input orcorresponding control signal, other type of corrections can be generatedas well. For example:

-   -   Thermal memory effect, which affects the response of the        amplifier due to accumulation of internal heat generated in        response to the RF input signal level (amplifier hitting peak        currents and voltages as a function of the RF input signal and        the envelope) and frequency content can be predicted based on        the RF input (e.g. integration of the envelope signal, running        power average of the RF input signal, etc. . . . ) and thus can        be compensated.    -   Heat generated within the amplifier as a consequence of the        output power requirement and/or environmental conditions, which        also affects the response of the amplifier, can be monitored        (e.g. thermo-coupler, FIG. 74) and corrections be generated as a        consequence.

In such cases, the lookup tables described above may include additionaldimensions to describe corrections based on the real time and/orestimated operating temperature of the amplifier. The person skilled inthe art will see that same correction/compensation method can be usedwith respect to other parameters which may affect operation of theamplifier. FIG. 74 (further described later) shows the case where atemperature detection module (920) is used to monitor the real timeoperating temperature of the amplifier and feed this information back toa control unit (801) within a controller (720) (e.g. Transceiver unit)which in turn uses this information to control operation of a waveformgeneration module (810, 820). Latter waveform generation module in turngenerates a control signal for the ETPS (180) supplying the amplifier(750). In a same manner and concurrently, transducer (930) may be usedto correct/compensate for the parameter it is monitoring. This parametermay be any measurable within the amplifier, such as various thresholdvoltages, bias currents, bias voltages and other measurable parametersassociated to the various components within the IC. The person skilledin the art will know about the batch to batch variability in ICmanufacturing process and thus will appreciate the added value of thepresented embodiment.

Going back to FIG. 1, the person skilled in the art will understand thatthis figure does not depict all the features described above and thatadditional circuitry may be used to accommodate for said features.

The envelope tracking amplifier (100) shown in FIG. 1 can be used as adriver, a final, or any other type of amplifier. The person skilled inthe art will understand that the stack may comprise any number of FETs,as the embodiment shown in FIG. 1 uses three FETs merely as an example.

FIG. 53 shows an embodiment according to the present disclosure wherethe control signal (190) of FIG. 1 is explained in additional detail.Shown in FIG. 53 are an input node (710), a transceiver (720) whoseinput is connected to the input node (710), a digital to analogconverter (DAC) (730) that is controlled by the transceiver (720), theenvelope tracking amplifier (100) of FIG. 1, and an output node (760)that corresponds to an output of the envelope tracking amplifier (100).

For the sake of simplicity, the transceiver (720) of FIG. 53 is depictedin a transmit mode, wherein the Input Data presented to its inputterminal (710) is processed within the transceiver to generate theanalog output data signal RFin which is usually modulated in one of manytransmission schemes, and fed to the input terminal (105) of theamplifier (100), wherein the RFin signal is further processed prior tofinal transmission. The input to the transceiver can be in analog ordigital form. The analog signal will typically be in I&Q or Cartesianformat. The envelope of the signal can be computed within thetransceiver as SQRT(I^2+Q^2) which is the magnitude of the vectorrepresented by (I,Q) components. If the data to the transceiver (720) isinput in a digital form, the envelope can be computed within thetransceiver (720) digitally or with analog techniques after the digitalinformation is converted to analog in the RF modulation process. Theperson skilled in the art will understand that by virtue of its internalprocessing capability the transceiver (720) has other functions andconnections besides what depicted in FIG. 53. It should also be notedthat similar to the manner in which the transceiver (720) performs thetask of converting the input data to the output analog stream RFin, ifenabled by some design changes it can perform additional operationsbased on the input data and/or the RFin. In turn this generatesadditional output signals with known relationships with respect to thesetwo signals. For example, if enabled by some design changes, thetransceiver (720) can generate and output:

-   -   Analog waveforms with known phase and amplitude relationships        with respect to RFin.    -   Analog waveforms with known phase and amplitude relationships        with respect to the dynamic envelope of RFin.    -   Completely arbitrary analog waveforms.    -   Digital representation of any of the above, which can be derived        either from RFin, directly from the input digital data or        neither (case of arbitrary waveform).

In the embodiment shown in FIG. 53, the transceiver (720) is modified tooutput a digital representation of the envelope amplitude of RFin alongwith the control signals, which are fed to the external DAC unit (730).The DAC (730) uses its input digital signals, comprised of data andcontrol signals, to generate an analog signal representing the envelopeamplitude of the input RFin, which in turn is fed to the ETPS (180)input control terminal (190). The ETPS (180) uses the analog signal fedto its control terminal (190) as a means to control the various supplyand biasing voltages fed to the amplifier (750) with the overall goal tooptimize dynamic operation of the amplifier. For example, referring toFIG. 1, the ETPS (180) uses input (190) to generate a dynamic voltagewith high current capability to feed transistor (155) drain terminal viainductor (170) and uses the same input (190) to generate a dynamicvoltage with lower current capability to feed the gate terminals oftransistors (120) and (155) via resistor (175). It is to be noted thatthe DAC unit (180) can also include a filter element at its outputstage, so to filter out any undesired artifacts introduced by thedigital-to-analog conversion process as well as to match input signalrequirements to the ETPS (180).

FIG. 54 shows another embodiment according to the present disclosurewherein the DAC unit (730) of FIG. 53 is now replaced with module (740).Module (740) is connected at its input to the transceiver (720) and isconnected at its output to input terminals (190) and (100 b) of theenvelope tracking amplifier (100). Module (740) is comprised of aplurality of DAC units, each similar in function to DAC (730) and eachwith a different set of input digital signals, comprised of data andcontrol signals, generated by the transceiver (720).

Similar to the embodiment of FIG. 53, each of the DAC units comprisedwithin the module (740), uses its input digital signals to generate ananalog signal representing the envelop amplitude of the input RFin,which in turn is fed to one of the plurality of input nodes within inputterminals (190) and (100 b), thus providing the envelope trackingamplifier (100) with a plurality of analog control voltages internallyused to set various supply and biasing voltages for optimal dynamicresponse of the amplifier. Compared to the embodiment of FIG. 53, thisapproach has the flexibility to generate analog control voltages withvarying amplitude and phase relationships with respect to each other andwith respect to the recovered envelope signal. Similar to the DAC unit(730) of FIG. 53, each of the DACs within module (740) can also includea filter element at its output stage, and which can be different foreach DAC unit.

In one embodiment of FIG. 54 and with reference back to FIG. 8, terminal(190) is used to feed (low current) control voltage to dedicatedcircuitry within the ETPS unit wherein high current drain voltage fortransistor (155) is generated, whereas terminal (100 b) is used todirectly feed the various gate bias voltages of the cascode transistorsas depicted by FIG. 8. Note that in this configuration, resistors (130),(140) and (175) previously shown in FIG. 1 are not present, as usage ofthese resistors may be dictated by the driving requirements of thedriving circuitry. In another embodiment of FIG. 54, control voltage at(190) is used to generate gate and drain bias voltages within the ETPSunit (180) while control voltages at (100 b) are used to provideincremental corrections to gate bias voltages (e.g. FIG. 9) via summingresistors connected to ET_(G1), ET_(G2) and ET_(G3).

It should also be noted that the ETPS, as used throughout the presentdisclosure, needs to have sufficient bandwidth to accommodate thebandwidth of the amplitude component of the modulation, which istypically 5-10 times wider than the modulation bandwidth. The ETPS musthave minimal distortion (amplitude and phase) over this bandwidth. It iscommon for the ETPS to be built using a DC-DC converter to provide thelow frequency portion of the amplitude path and an analog amplifier forthe high frequency portion, along with some analog control circuitry tocontrol overall operation of the unit. The DC-DC converter has a higherefficiency than the analog amplifier, but suffers from challenges inbandwidth as well as spurs due to the switching nature of the DC-DC. Theanalog amplifier covers the DC-DC converter's shortfalls. Noise, inaddition to the spurs, must also be considered. A faster DC-DC converterwill improve the overall efficiency of the ETPS by requiring less helpfrom the analog amplifier. In the limit case, the ETPS consists ofsolely of a DC-DC converter. Using a semiconductor process such assilicon on sapphire (SOS), or even silicon on insulator (SOI), reducesthe parasitic capacitances and offers several device advantages thatresult in faster DC-DC converters.

FIG. 55 shows another embodiment according to the present disclosurewherein a wave shaping unit is used to further generate independentanalog control signals which are in turn used to feed various bias andsupply voltages within the envelope tracking amplifier (100). In thisembodiment, the DAC (730) output is connected to the input of the waveshaping unit (780A) which in turn through its plurality of outputs isconnected to the envelope tracking amplifier (100) input terminals (190)and (100 b), the latter input terminal being comprised of a plurality ofinput nodes. The wave shaping unit receives a single input voltage fromthe DAC unit (730), which is typically representative of the envelopeamplitude of the RFin signal fed to the amplifier (100) at terminal(105), and it is programmed to generate using its internal waveformprocessing capability (e.g. analogue/digital signal processing, lookuptables), a set of independent output voltages based on the inputvoltage, with varying amplitude and phase relationships. Theserelationships, designed to further improve overall dynamic response ofthe amplifier (100) are either pre-programmed within the wave shapingunit or can be defined dynamically through a control input terminal(780B) to the wave shaping unit. Control data fed to the input terminal(780B) may originate from transceiver unit (720) or a separate controlunit and may include information such mode/configuration selection andadjustments to the waveform processing such as offsets, gain and phase.

As it was the case in the embodiment depicted by FIG. 54, controlvoltages fed to terminals (190) and (100 b) of the embodiment depictedby FIG. 55 can be internally used by the envelope tracking amplifier(100) in different ways and as supported by the internal electricalconfiguration of the amplifier (i.e. FIGS. 8 and 9).

The examples set forth above are provided to give those of ordinaryskill in the art an overview of various control systems and methodsrelated to the implementation of the envelope tracking method as relatedto the present disclosure. As mentioned before, these are onlyimplementation examples and not limiting the scope of what the inventorsregard as their disclosure.

Based on these examples, one can derive the following set of functionalunits and system functions to be implemented therein through somededicated circuitry, which together implement the envelope trackingmethod. Any combination of these functional units may be integrated inone IC and/or module.

Functional Units:

-   -   Transceiver (Tx/Rx)    -   ET power supply (ETPS)    -   Power Amplifier (PA)    -   Waveform shaping unit (WS)        System Functions:    -   Envelope detection:        -   Generates a representation of the envelope signal in either            digital or analog form based on the analog or digital Data            input or the RFin signal.    -   Gate waveform generation:        -   Generates a representation of the Gate bias control signal            in either digital or analog form. This is generally based on            the envelope signal and a set of ET amplifier operating            characteristics.    -   Drain waveform generation:        -   Generates a representation of the Drain bias control signal            in either digital or analog form. This is generally based on            the envelope signal and a set of ET amplifier operating            characteristics.    -   PA gate input generation:        -   Generates the actual analog gate bias voltage to be fed to            each of the gates of the cascode amplifier. This is            generally based on the gate waveform generated by the gate            waveform generation function and adapted to match input            requirements to the various gates.    -   PA drain input generation:        -   Generates the actual analog drain bias voltage to be fed to            the cascode amplifier. This is generally based on the drain            waveform generated by the drain waveform generation function            and adapted to match input requirements to the drain.

The person skilled in the art will understand that known designtechniques are available for implementation of the presented systemfunctions. For example:

-   -   Envelope detection=SQRT(I^2+Q^2) or diode envelope detector.    -   Waveform generation=lookup table (FIGS. 71, 72), digital        processing using DSP (FIG. 73) or analog processing such as        op-amp circuits to adjust gain, DC offsets, etc. . . . .    -   Input generation=D/A converter if needed plus buffer amplifiers        to present appropriate impedance/drive strength.

The various examples set forth above represent some possibleimplementations of the envelope tracking method by placing such systemfunctions in newly defined modules (i.e. 730, 740, 780A) and/or inspecific functional units. As such, the input/output configurations ofsaid units reflect the chosen implementation. For example, input to thePA unit (750) is modified in order to adapt to each of theconfigurations of FIGS. 53-55. To allow direct input to each of the gatebias voltages, ladder resistors used in FIG. 1 to provide (combined)gate biasing, is removed as depicted in FIG. 8. On the other hand and asdepicted in FIG. 9, to allow incremental corrections to each of the gatebias voltages, input summing resistors were added to the PA. In anotherexample, the transceiver unit (720) in FIG. 53 outputs one set ofdigital data to the DAC unit (730), whereas the transceiver unit (720)in FIG. 54 has to adapt to the plurality of DAC units within (740) andthus outputs several set of digital data.

Furthermore, a person of ordinary skill will understand that any of suchsystem functions can be implemented within a plurality of functionalunits given some design modification to said unit. For example, thetransceiver can be made to perform envelope detection based on its inputdata at terminal (710), but so can the PA unit based on the input RFinsignal at terminal (105), or the waveform shaping unit (780A) of FIG. 55based on its input from DAC (730). One can also envision a transceiverunit performing envelope detection and gate/drain generation, or an ETPSperforming these same system functions.

This apparent flexibility of mixing and matching system functions withinfunctional units, and adapting I/O's accordingly, is however limited bythe choice of good and sound design principles and integration. Forexample, any integration of waveform generation into the PA isbeneficial because monolithic integration means the waveform signalswill be matched and the amplitude/phase response will be wellcontrolled. In contrast, splitting the gate and drain waveformgeneration across multiple ICs and packages introduces potentialamplitude, phase and delay issues subject to PCB design and partvariation. In another example and as previously mentioned, due to itshigh current requirement, it is desirable to keep the drain voltagesupply generation close to the PA unit and within the ETPS, since latteris designed for high currents and good heat dissipation. This in turnlimits the PA input configuration for its drain bias to an analog input,in contrast to a possible digital input for the gates biases, wherebyinternal D/A conversion units can generate the analog gate biasvoltages.

Given the above, Table 1 is a proposed embodiment of design andintegration constraints for the system functions. It defines possiblefunctional integrations for each of the system functions.

TABLE 1 Functional Input I/O Signal Unit Source Type Envelope Tx/Rx,ETPS, RFin/Analog Analog/Digital detection PA, WS Data/Digital data Gatewaveform Tx/Rx, ETPS, Envelope Analog/Digital generation PA, WSDetection Drain waveform Tx/Rx, ETPS, Envelope Analog/Digital generationPA, WS detection PA Drain input ETPS Drain Analog/Digital generationwaveform Input Analog generation Output PA Gate input Tx/Rx, ETPS, GateAnalog/Digital generation PA, WS waveform Input Analog generation OutputAs per Table 1, the following constraints are defined:

-   -   Envelope detection can be performed within any of the functional        units and corresponding module is required to have one of RFin,        Analog input data or Digital input data as input. Its input and        output can be in either analog or digital form.    -   Gate waveform generation can be performed within any of the        functional units and corresponding module is required to be        connected to the functional unit performing the envelope        detection. Input and output signals can be analog or digital.    -   Drain waveform generation can be performed within any of the        functional units and corresponding module is required to be        connected to the functional unit performing the envelope        detection. Input and output signals can be analog or digital.    -   PA Drain input generation is required to be performed within        ETPS unit which is required to be connected to the Drain        waveform generation module. Input signal to corresponding module        can be analog or digital, and output signal is analog.    -   PA Gate input generation can be performed within any of the        functional units and corresponding module is required to be        connected to the Gate waveform generation module. Input signal        to corresponding module can be analog or digital, and output        signal is analog.

FIG. 56 breaks down the controlling elements for the envelope trackingsystem. Herewith new modules (805, 810, 820, 830, 840) are introducedwhich implement the system functions previously mentioned and aredepicted accounting for restrictions presented in table 1. So forexample, as per table 1, the Drain Input generation module (840) isplaced within the ETPS unit (180), has a single output signal (uncrossedoutput line) which feeds the ET_(D) input of the power amplifier (750)and its input is connected to the Drain Waveform generation module (810)via several signal lines (so could be several digital input signals orsingle analog input signal).

Modules presented in FIG. 56 are drawn individually and not assigned toany of the functional units at this point. Exception to this being theDrain Input generation module (840) which is integrated within ETPS unit(840) as per table 1. Furthermore, the ETPS can be subdivided into ananalog control part, a DC-DC and an analog amplifier or error amplifier.These pieces can be broken apart and combined with various blocks aswell.

In FIG. 56 the envelope detection module (805) takes its input fromeither the Input Data at input terminal (710) which feeds thetransceiver unit (720), or the modulated analog RFin signal generated bythe transceiver unit and fed to the input terminal (105) of theamplifier unit (750). Therefore the envelope detection module (805) mayhave one (analog RFin) or several (Input Data) signal lines at its inputport. In turn the envelope detection module (805) provides an analog ordigital representation of the envelope signal to the Drain Waveform(810) and Gate Waveform (820) generation modules, so again, thesemodules may have one analog or several digital input signal lines. TheDrain Waveform generation module (810) in turn feeds the Drain Inputgeneration module (840), placed within the ETPS unit (180), via inputterminal (190). Finally Drain Input generation module (840) feeds thedrain of the amplifier (750) at node ET_(D) through inductor (170) withan analog voltage. Concurrently and in a similar fashion, biasing analogvoltages for gates to ET_(G1), ET_(G2) and ET_(G3) are generated withinGate Input module (830) and routed to amplifier (750) via input terminal(100 b). It should be noted that the usage of the term “gate input”should not be seen as a limitation of the present embodiment, or otherembodiments of this disclosure, to only FET devices, as the skilledperson will know how to apply these teachings to other type of devices(e.g. replace “gate input” with “base input” for the case of a bipolardevice configuration).

FIG. 56 therefore represents the envelope tracking system, which includethe functional units; transceiver (720), ETPS (180) and amplifier (750),and the enabling system functions each represented by a dedicated systemmodule wherein the circuitry to generate the specific function resides.Any of the FIGS. 53-55 can be represented using these system modules andfunctional units, wherein as previously mentioned, Input/Outputconfiguration of each module is tailored to the specific configuration.

For example, FIG. 57 is a representation of embodiment of FIG. 53highlighting the system functions. The envelope detection module (805)and the Drain/Gate Waveform generation modules (810, 820) reside withinthe transceiver unit (720), and Drain/Gate Input generation modules(840, 830) reside within ETPS (180) and amplifier (750) respectively.Internal amplifier (750) configuration is as depicted by FIG. 1, whereingate biases are derived via single input voltage from Gate Inputgenerator (830) fed to a ladder network comprised of resistors (130,140, 175). DAC unit (730) is used to translate digital envelope datafrom Drain/Gate waveform generator module into analog form prior tofeeding to the Drain/Gate input generator modules residing within ETPSunit (180) and amplifier (750). To be noted that in this embodiment, asingle waveform is generated for both drain and gate control, therebyreducing Drain/Gate waveform generation to a single module. Input to theenvelope detection (805) is the Input Data at input terminal (710), butcould also be the RFin signal generated within the transceiver unit(720). A person of ordinary skill in the art will understand that FIG.60 embodies the same envelope tracking method as depicted by FIG. 53 andthus FIG. 57. In FIG. 60 functionality of the DAC unit (730) is moved tothe transceiver unit (720) and merged with the Drain/Gate generationmodule becoming the output stage of the module. Therefore FIG. 60represents same embodiment as depicted in FIG. 53 but using the definedfunctional units and modules while maintaining overall systemfunctionality. Alternatively, the DAC unit (730) may be placed withinETPS (180) or within the envelope tracking unit (100), as depicted inFIG. 61, in which case the input terminal (190) is modified to adapt tothe multiple input signals required to interface with the DAC unit(730).

Equivalently, FIG. 58 represents same embodiment as FIG. 54 wherein thesystem functions are highlighted. Drain/Gate Waveform generation isperformed within transceiver unit (720), but in this case using twodistinct system modules, one dedicated to the Drain Waveform generation(810) outputting a single digital data set to DAC1, and the otherdedicated to the Gate Waveforms generation (820) outputting differentdigital data sets to each of the dedicated gate DACs (DAC2-4). In thisembodiment Drain Input generation (840) remains within ETPS unit (180)whereas the task of Gate Input generation is performed by DAC2-4, whichthrough input terminal (100 b) respectively feed biasing gates voltagesto ET_(G1), ET_(G2) and ET_(G3). Going one step further, FIG. 62represents again same embodiment as FIG. 54 using only the functionalunits and modules. This is done by repartitioning functionality withinmodule (740) into system modules and then mapping these into functionalunits. As such, DAC1 becomes the output stage of Drain Waveformgeneration module (810) which is moved within transceiver unit (720) andDAC2-4 become the Gate Input generation module placed within thetransceiver. In this implementation all envelope tracking relatedcontrol signals between transceiver unit (720) and envelope trackingamplifier (100) are in analog form. On the other hand and as depicted byFIG. 63, by shifting module (740) functionality entirely within ETPS(180) and amplifier (750), tracking related control signals between thesame two units become all digital. Finally (740) functionality can besplit between transceiver unit (720) and ETPS (180) as depicted in FIG.64 to obtain a hybrid configuration whereby a mix of analog and digitaltracking related control signals exist between transceiver unit (720)and envelope tracking amplifier (100). Of course for each of thesecases, I/O configuration for the functional units adapt to the requiredinterface type.

System functions of embodiment presented in FIG. 55 are highlighted inFIG. 59. Wave Shaping unit (780A) contains Drain and Gate Waveformgeneration modules (810, 820) which have a common input from DAC unit(730), as well as the Gate Input generation module (830) which feeds thegate bias voltages via input terminal (100 b) to ET_(G1), ET_(G2) andET_(G3). Drain Waveform generation module (810) feeds via input terminal(190) the gate control signal to the Drain Input module (840) withinETPS (180). This configuration can be further reduced to contain onlyfunctional units by mapping functionalities within the Wave Shaping unit(780A) and the DAC unit (730) into the functional units. As seen inprior examples, this can be performed in various ways, all yielding tosame overall system functionality and each imposing some type of I/Ointerface adaption for each functional unit. By mapping all saidfunctionalities into the transceiver unit (720), the systemconfiguration of FIG. 65 is obtained, wherein envelope tracking controlsfrom transceiver (720) to envelope tracking amplifier (100) are inanalog form. By mapping all said functionalities into the envelopetracking amplifier (100), then the controls are in digital form asdepicted by FIG. 66. Finally, by partitioning said functionalities andmapping into both the transceiver unit (720) and the envelope trackingamplifier (100), then system configuration of FIG. 67 is obtained,wherein a single analog control line is transmitted from the transceiverunit (720) and the envelope tracking amplifier (100).

As a summary, in the previous paragraphs, various system levelembodiments for controls and methods implementation of the envelopetracking amplifier using some functional units; the transceiver unit(720), the ETPS unit (180) and the amplifier unit (750), surrounded bysome external enabling modules (730, 740, 780A) were presented.Subsequently a set of enabling system functions required to generate thepresented embodiments as well as associated design constraints weredefined which together allowed to define a generic system configurationfor the envelope tracking method and controls thereof (FIG. 56). Latterconfiguration was used to create specific configurations reflecting eachof the embodiments presented in the first section using only functionalunits and system modules. In the course of this exercise it wasdemonstrated that for a given proposed embodiment, several suchconfigurations exist and presented some, but not all, as these are wellwithin the reach of the person skilled in the art. Although at thesystem level these configurations are equivalent, in practice each maypose different issues as far as manufacturing, performance andreliability of the finished product. These issues are of course outsidethe scope of the present disclosure and as such shall not be discussedherewith in too much detail.

FIG. 68 shows a practical implementation of the current embodimentwherein a driver ET amplifier (750 a) is used to drive the final stage(750). In this embodiment a single ETPS (180) feeds biasing supplies(e.g. drains and gates) to both amplifiers. In this configuration bothamplifiers may be of types depicted in FIGS. 8 and 9, with systemconfiguration for each of the ET amplifiers further depicted by FIG. 60.The person skilled in the art will notice limitation associated with theconfiguration of FIG. 68, wherein by virtue of a shared supplyconnection to both amplifiers, RF interference/coupling may arisebetween the two amplifiers, thus degrading overall system performance(e.g. ACLR, linearity, efficiency), as well as possibly induceoscillation. This shortcoming is addressed in FIG. 69, wherein accordingto the presented embodiment, the ETPS (180) is modified to comprise twodecoupled and isolated output supplies, each dedicated to one of the ETamplifiers.

It should be noted that in the case of an ET implementation, traditionalfiltering of the supply input to the amplifier via a large bypasscapacitor to reduce feedback between the various amplification stages,and thus possible oscillation, is not possible, since such a capacitorwould distort the supply envelope modulation and thus the RF output, aswell as reduce any efficiency improvement obtainable from the ET design.FIG. 69A shows one possible embodiment for decoupling the two outputs ofthe ETPS (as discussed in the prior paragraph), thus minimizing saidperformance issues and possible oscillation. The filter (755) isdesigned to pass DC and the envelope modulation frequency and stophigher frequencies which can cause the combination of driver and finalstage to oscillate. The filter components L1 and C1 break theoscillation loop while allowing ET to function. Given the teachings ofthis embodiment, the skilled person will find other possible filteringimplementations, not necessarily reduced to the filter as depicted byFIG. 69A, which thus should not be considered a design limitation.

The person skilled in the art will now notice that the embodimentspresented in FIGS. 68 and 69 provide a single control to the ETPS (180),thus limits the flexibility to independently control operation of eachET amplifier (750, 750 a). This shortcoming is addressed in FIG. 70,wherein according to the presented embodiment two dedicated andindependent ETPS (180, 180 a) are used to each supply ET amplifiers(750, 750 a) respectively. By virtue of their independent controlsprovided at (190, 190 a), each ETPS can be independently controlled andthus independently affect operation of the corresponding ET amplifierfor better overall system performance. Although these embodimentspresented in conjunction of an ET pair (driver/final) have used a basesystem configuration depicted by FIG. 60, the person skilled in the artwill know how to use other system embodiments disclosed herewith for thecase where two or more cascaded amplifiers are used. FIG. 70A is oneexample embodiment of the embodiment presented in FIG. 70, whereamplifiers (750, 750 a) are shown in detail.

Embodiments as depicted by FIGS. 68-70 can provide undesirable couplingissues between the two amplification stages (driver, final).Specifically, when the envelope modulation signal of the driveramplifier supply (generated by ETPS (180)) is coupled to the input ofthe final stage amplifier (750), distortion of the output RF signal canbe observed. Traditional circuit layout techniques such as physicalseparation of components and electrical isolation via ground shieldingmay not suffice to reduce the unwanted coupling, as the unwanted signalmay be coupled via the conduction coupling path between the output ofthe drive and the input of the final amplifier which conducts the RFsignal (conduction path between output of (750 a) and input of (750)).As per further embodiment of the present disclosure and as depicted byFIG. 70B, such unwanted coupling within the said conduction coupling isreduced by adding a frequency selective filter (750 b) within theconduction coupling path that will remove the envelope modulationsignal, and thus reduce distortion of the output RF signal. It should benoted that such a technique is possible since the (lower frequency)envelope signal spectrum resides outside the RF signal spectrum. In analternative embodiment, the frequency selective filter (750 b) may bereplaced by the notch filter (750 c), specifically designed to notch outthe envelope modulation signal present in the conduction path.

As described earlier, close proximity of the ETPS unit to the amplifierunit is desirable, such as to reduce any phase/amplitude degradation ofthe envelope supply to the amplifier unit, as the supply directlyaffects the output of the amplifier. As such, monolithic integration ofthese two units, using for example Silicon on Insulator technology,which allows for high transistor stacks (e.g. 3, 4 or greater) andhigher breakdown voltages, is disclosed. This integration also allowsfor better stability when feedback is used around the amplifier as allthe components affecting the output may be integrated.

FIG. 74 shows a system configuration according to the present disclosurewherein various optimization modules are embedded within the amplifierunit (100). Although the amplifier unit is depicted containing a singleET amplifier, as discussed earlier, several cascaded amplifiers with orwithout dedicated ETPS may also be used. Furthermore, ETPS and ETamplifiers may be monolithically integrated (e.g. Silicon on Insulator)for better overall performance. The integration would allow easierinterfacing of numerous dynamically biased nodes, far more than if thecomponents were not integrated due to the large number of I/O. Forexample, a 2-stage amplifier (e.g. driver and final) that contains astack of 3 devices could have 6 different gate voltages plus 2 differentdrain voltages to generate and interconnect. Routing of these 8 signalswould be difficult without integration. Integration also greatlybenefits the integrity of these interface signals. Keeping the signalson chip preserves the interface conditions and minimizes parasiticeffects that can load down the signal, shift the phase of the signal,and introduce cross-talk or signal isolation concerns.

The presented optimization modules may be used in different context andfor optimizing different parameters at different stages of operation.For example, the temperature detector module (920), may be used duringamplifier transmission and provide feedback to main controller ofoperating temperature, which may prompt the controller to modifycontrols (supplies or other amplifier configuration related) to theamplifier. Such controls may cause for example selection of differentwaveforms for the ETPS unit to shift biasing or supply of the amplifierin a manner to maintain a specific response characteristic (e.g. ACLR,linearity, efficiency, power output, etc. . . . ). If lookup tables areused in the waveform generation module, controls may result in selectionof a different lookup table in response to a temperature shift detectedby the temperature detection module. In other cases, controls may promptinjection of a compensation error component (e.g. offset, gain) into thewaveform generation module. Other parameters can be monitored and usedto drive the configuration and control loop. Examples include detectingthreshold voltages of devices in the PA IC or ETPS or other relatedcircuits, detecting voltage and current levels, input or output power,and the status/health of circuits and devices. Monitoring informationsuch as this can be used to drive a configuration setting (slow changes,for example at power up) or in a real-time closed loop system.

Another optimization module, the Non-Volatile RAM module (910), may beused in different manners. For example during the manufacturing stage ofthe amplifier unit (100), module (910) may be programmed to containcharacteristic data specific to the amplifier unit, not only vis-à-visbiasing and supply variation, but also with respect to temperature andother parameters. In turn, during final integration of the amplifierunit into a target device (e.g. cellular phone), NV-RAM content is usedto expedite calibration, testing and troubleshooting of the targetdevice. Availability of data within module (910) not only expeditescalibration/testing/troubleshooting of the target device, possiblyallowing bypass of certain steps required in the absence of the dataprovided by the NV-RAM, but also guarantees that the final device is“optimized” for operation with respect to the specific amplifier unit,thus rendering issues associated with batch to batch manufacturingvariability moot. During operation of the device, the NV-RAM content canalso be used to provide correction factors based on operating conditions(e.g. temperature and other). The person skilled in the art willunderstand the flexibility of providing such a programmed NV-RAM coupledwith a temperature detector or some other type of transducer (930), andwill be able to use teaching from the present disclosure to adapt tovarious conditions and requirements. In some embodiments, thiscalibration can be done at factory test of the PA, the ETPS, the PA+ETPSif integrated, factory test of the radio system, or in-situ by detectorsin the radio system. The calibration can also be based oncharacterization. Typical parameters that would be monitored during thecalibration process include output power, gain, AM-AM, AM-PM, ACLR, EVM,receive band noise, efficiency, and voltage levels.

Although throughout the present disclosure envelope tracking was used asan amplification method in the various embodiments, it should be notedthat the techniques for stacking, mode switching optimization, andsystem partitioning used in said embodiments apply to envelope trackingas well as envelope following, polar amplifiers/systems, and averagepower tracking described in the early sections of this disclosure. Thesetechniques can be further applied in conjunction with other amplifierefficiency improvement and performance techniques such as analogpre-distortion, digital pre-distortion, Doherty amplifiers, LINC oroutphasing amplifiers, switching amplifiers such as Class S and Class M,and also distributed amplifiers, among others. The skilled person willthus appreciate the flexibility and adaptability of the variousembodiments of this disclosure to other known configurations andtechniques.

Finally, as integration is usually synonymous to reduced cost andreduced form factor, it is envisioned, as another embodiment of thecurrent disclosure, that the entirety of the components of FIGS. 53-74be monolithically integrated (e.g. Silicon on Insulator), with variousintermediary stages, wherein partial integration of the components isperformed.

The examples set forth above are provided to give those of ordinaryskill in the art a complete disclosure and description of how to makeand use the embodiments of the control systems and methods for poweramplifiers operating in envelope tracking mode of the disclosure, andare not intended to limit the scope of what the inventors regard astheir disclosure. Such embodiments may be, for example, used withinmobile handsets for current communication systems (e.g. WCMDA, LTE, etc.. . . ) wherein amplification of signals with frequency content of above100 MHz and at power levels of above 50 mW may be required. The skilledperson may find other suitable implementations of the presentedembodiments.

Modifications of the above-described modes for carrying out the methodsand systems herein disclosed that are obvious to persons of skill in theart are intended to be within the scope of the following claims. Allpatents and publications mentioned in the specification are indicativeof the levels of skill of those skilled in the art to which thedisclosure pertains. All references cited in this disclosure areincorporated by reference to the same extent as if each reference hadbeen incorporated by reference in its entirety individually.

It is to be understood that the disclosure is not limited to particularmethods or systems, which can, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification and the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontent clearly dictates otherwise. The term “plurality” includes two ormore referents unless the content clearly dictates otherwise. Unlessdefined otherwise, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which the disclosure pertains.

A number of embodiments of the disclosure have been described.Nevertheless, it will be understood that various modifications can bemade without departing from the spirit and scope of the presentdisclosure. Accordingly, other embodiments are within the scope of thefollowing claims.

The invention claimed is:
 1. A system for affecting operation of anenvelope tracking (ET) amplifier, comprising: an ET amplifier configuredto receive an RF input signal and generate therefrom, an RF outputsignal based on a response of the ET amplifier, the ET amplifiercomprising an amplifier unit wherein the amplifier unit comprises aplurality of stacked transistors operatively coupled to a plurality ofbias terminals adapted to receive a set of analog input-control signals;a set of operating parameters defining the response of the ET amplifier;and a control circuit adapted to detect an envelope of the RF inputsignal and generate, based on said envelope signal, the set of analoginput-control signals that is provided to the ET amplifier for affectingthe response according to the set of operating parameters.
 2. The systemof claim 1 wherein the plurality of bias terminals comprise a pluralityof gate terminals of the plurality of stacked transistors and a drainterminal of an output transistor of the amplifier unit.
 3. The system ofclaim 2 wherein the set of analog input-control signals comprise aplurality of gate-input-control signals and a drain-input-controlsignal, such as the plurality of gate-input-control signals are providedto the plurality of gate terminals, and the drain-input-control signalis provided to the drain terminal.
 4. The system of claim 3 wherein thecontrol circuit further comprises: an envelope detection circuit adaptedto detect the envelope of the RF input signal and generate acorresponding envelope signal; a waveform generation circuit configuredto receive the envelope signal and adapted to generate a set of waveformsignals based on the envelope signal and the set of operatingparameters, and an input generation circuit configured to receive theset of waveform signals and adapted to output therefrom the set ofanalog input-control signals.
 5. The system of claim 4 wherein thewaveform generation circuit further comprises: a gate-waveformgeneration circuit configured to receive the envelope signal and adaptedto generate a set of gate-waveform signals based on the envelope signaland the set of operating parameters, and a drain-waveform generationcircuit configured to receive the envelope signal and adapted togenerate a drain-waveform signal based on the envelope signal and theset of operating parameters.
 6. The system of claim 5 wherein the inputgeneration circuit further comprises: a gate-input generation circuitconfigured to receive the set of gate-waveform signals and adapted togenerate therefrom the plurality of gate-input-control signals, and adrain-input generation circuit configured to receive the drain-waveformsignal and adapted to generate therefrom the drain-input-control signal.7. The system of claim 6 wherein the ET amplifier further comprises avariable power supply unit wherein the variable power supply unit isconfigured to operatively comprise the drain-input generation circuit.8. The system of claim 7 wherein the drain-input generation circuit is aDC-to-DC converter.
 9. The system of claim 8 wherein the DC-to-DCconverter is fabricated using one of: a) silicon on sapphire (SOS)technology, and b) silicon on insulator (SOI) technology.
 10. The systemof claim 7 wherein the amplifier unit further comprises a cascadedseries of amplifiers operatively coupled in series, wherein eachamplifier unit comprises a plurality of stacked transistors operativelycoupled to a plurality of bias terminals adapted to receive the set ofanalog input-control signals.
 11. The system in claim 10 wherein thecascaded series of amplifiers comprises a driver amplifier and a finalamplifier, each comprising a drain terminal in correspondence of anoutput transistor.
 12. The system of claim 11 wherein the drain-inputgeneration circuit provides the drain-input-control signal to the driveramplifier and to the final amplifier.
 13. The system of claim 12 whereinthe drain-input generation circuit provides isolated drain-input-controlsignals to each of the driver amplifier and the final amplifier.
 14. Thesystem of claim 12 further comprising an isolation filter, wherein theisolation filter is inserted within a conduction path between the drainterminal of the driver amplifier and the drain terminal of the finalamplifier.
 15. The system of claim 14 wherein the isolation filter isconfigured to pass a DC signal and a signal at a frequency of theenvelope signal.
 16. The system of claim 14 wherein the isolation filtercomprises an inductor in parallel with a capacitor.
 17. The system ofclaim 11 further comprising a second drain-input generation circuit,such as each of the two drain-input generation circuits provides anindependent drain-input-control signal to each of the driver amplifierand the final amplifier.
 18. The system of claim 17 further comprising asecond variable power supply unit comprising the second drain-inputgeneration circuit.
 19. The system of claim 10 or claim 11 furthercomprising a frequency selective filter operatively coupled in seriesbetween an output terminal of an amplifier of the cascaded series ofamplifiers and an input terminal of a following amplifier.
 20. Thesystem of claim 19 wherein the frequency selective filter is configuredto attenuate a signal at a frequency of the envelope signal.
 21. Thesystem of claim 20 wherein the frequency selective filter is a notchfilter.
 22. The system of claim 7 further comprising a transceiver unitconfigured to generate the RF input signal from a baseband data, whereinthe combination of the transceiver unit, the variable power supply unitand the amplifier unit is configured to operatively comprise theenvelope detection circuit, the gate-waveform generation circuit, thedrain-waveform generation circuit, and the gate-input generationcircuit.
 23. The system of claim 22 wherein the transceiver unit isfurther configured to operatively comprise at least one of: a) thedrain-waveform generation circuit, b) the gate-waveform generationcircuit; c) the gate-input generation circuit, and d) the envelopedetection circuit.
 24. The system of claim 22 wherein the variable powersupply unit is further configured to operatively comprise at least oneof: a) the drain-waveform generation circuit, b) the gate-waveformgeneration circuit; c) the gate-input generation circuit, and d) theenvelope detection circuit.
 25. The system of claim 10 wherein theamplifier unit is further configured to operatively comprise at leastone of: a) the drain-waveform generation circuit, b) the gate-waveformgeneration circuit; c) the gate-input generation circuit, and d) theenvelope detection circuit.
 26. The system of claim 22 wherein the setof operating parameters further comprises minimizing thermal memoryeffect of the amplifier unit.
 27. The system of claim 22 wherein thewaveform generation circuit further comprises circuitry configured topredict a temperature of the amplifier unit based on the RF input signaland provide a correction based on said predicted temperature such assaid correction is combined with an output of the waveform generationcircuit to further optimize response of the amplifier.
 28. The systemaccording to claim 1 wherein the ET amplifier further comprises atemperature detection circuit adapted to provide temperature data incorrespondence of the operating temperature of the ET amplifier to thecontrol circuit, and wherein the control circuit is adapted to furtheraffect the response of the ET amplifier based on the operatingtemperature.
 29. The system according to any of claim 7, 12 or 18,wherein the ET amplifier is monolithically integrated.
 30. The systemaccording to claim 29 wherein an insulated silicon on sapphire (SOS)fabrication or an insulated silicon on insulator (SOI) fabricationtechnology is used.
 31. A method for generating control signals toaffect operation of an ET amplifier based on a desired response, themethod comprising: providing an ET amplifier configured to receive adrain control signal and a plurality of gate control signals; generatingthe drain control signal based on an envelope signal of an RF input tothe ET amplifier; correlating a response of the ET amplifier with theplurality of gate control signals and the drain control signal;generating a correlation table based on the obtained correlation;selecting operating parameters for a desired response of the ETamplifier; using the correlation table to generate a mapping tablebetween the drain control signal and the gate control signals for thedesired response; implementing control circuitry adapted to generate thegate control signals from the drain control signal using the mappingtable, and affecting operation of the ET amplifier by feeding the draincontrol signal and the mapped gate control signals generated by thecontrol circuitry to the ET amplifier.
 32. The method of claim 31wherein selecting of the operating parameters is based on at least oneof: a) maximizing linearity, b) maximizing efficiency, c) minimizingadjacent channel leakage ratio (ACLR), d) minimizing memory effects, ande) adjusting output power level.
 33. The method of claim 31 whereingenerating of the gate control signals comprises at least one of: a)using memory based lookup tables, b) using analog circuitry comprisingop-amps, and c) using digital circuitry.
 34. The method of claim 31wherein implementing of the control circuitry comprises at least one of:a) operatively fitting the entirety of the control circuitry within theET amplifier, and b) operatively fitting a portion of the controlcircuitry within the ET amplifier.
 35. The method of claim 31 furthercomprising correlating the response of the ET amplifier with a change inone or more operating conditions of the amplifier unit, and furtheraffecting operation of the amplifier by using said correlation.
 36. Themethod of claim 35 wherein the one or more operating conditionscomprises of a change in temperature.
 37. The method of claim 31 whereinthe ET amplifier further comprises a Non-Volatile RAM containing themapping table of the ET amplifier.